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GU No. 44* 


This' book should be returned on or qefore the date* 
last nterkcd below. 


Essential Oils 



Vice President and Technical Director 
Frib&che Brothers, Inc., New York, N. Y. 






D. Van Nostrand Company, Inc., 250 Fourth Avenue, New York 3 

D. Van Nostrand Company, (Canada), Ltd., 228 Bloor Street, Toronto 8 


Macmillan & Company, Ltd., St. Martin's Street, London, W.C. 2 

Copyright, 1048 



All rights reserved 

This book, or any parts thereof, may not be, 
reproduced in any form without written /n?r- 
mission from the author and the publishers. 

"The use in this volume of certain portions of the text of the United States Pharma- 
copoeia, Thirteenth Revision, is by virtue of permission received from the Board of Trustees 
of 'the United States Pharmacopoeial Convention. The said Board of Trustees is not 
responsible for any inaccuracy of quotation nor for any errors in the statement of quantities 
or percentage strengths." 

, Permission has been received to quote from the Official and Tentative Methods of A nalysis 
of the Association of Official Agricultural Chemists. 

"Permission to use for comment parts of the te\t of the National Formulary, Eighth 
Edition, in this volume has l>ccn granted by the committee on publications by authority 
of the council of the American Pharmaceutical Association/ 1 



President of 

Fritzsche Brothers, Inc., 

whose vision and generosity made this 

work possible 



Vice President and Technical Director of Fritzsche Brothers, 
Inc., New York, N. Y. 


Professor, Bio-organic Chemistry, California Institute of 
Technology, Pasadena, California. 


Director of Analytical Laboratories, Fritzsche Brothers, Inc., 
New York, N. Y. 

GEORGE URDANG, Ph.G., D.Sc. Xat., Sc.D. 

Director, American Institute of the History of Pharmacy, 
Madison, Wisconsin. 


The industry and science of essential oils have undergone within the 
last two decades more changes than could have been anticipated by those 
writers who, during the 1920's, contributed so valuably to our knowledge 
of this field. It is, therefore, no derogation of the works of Gildemeister 
and Hoffmann, Parry, Finnemore, and others, to state that the time is past 
due for bringing the whole subject up-to-date. This is the author's motive 
for the present treatise on the production, chemistry, analysis and appli- 
cation of these interesting and important products. It seems particularly 
fitting that this work be published in the United States, which, as the largest 
user of essential oils, lias the most vital concern in the progress and ex- 
pansion of the essential oil industry. 

Within the last ten years and largely as a result of World War II 
there have taken place fundamental developments within the field, especially 
with respect to new sources of supply in the Western Hemisphere. It has 
been the author's rare privilege to witness most of these developments at 
first hand. His travels for more than twenty years have taken him the 
length and breadth of Europe, through Africa, Asia, Australia, into the new 
producing centers of North, Central and South America in all of which 
places he surveyed the production of essential oils at their source. 

The original purpose of this systematic survey was to snpply Fritzsche 
Brothers, Inc., of New York, the essential oil industry in general, and Gov- 
ernment agencies with exhaustive data on the production of essential oils. 
In the course of this work the author collected countless samples of authen- 
tic oils, produced under his supervision and of guaranteed purity. These 
were shipped to his headquarters in New York and submitted to careful 
analysis, which permitted the establishment of certain criteria of purity for 
many hitherto dubious oils. The results of such work have appeared in a 
series of articles published in leading trade journals during the last twenty 
years, for the information and guidance of those engaged in the production 
and in the use of these materials. 

As the work progressed, the author was repeatedly urged to publish his 
data in their entirety, so that they might be readily accessible in compre- 
hensive and up-to-date form. He has at last, therefore, attempted to com- 
bine in this work his own observations in the field, the seventy-five years' 
experience of Fritzsche Brothers, Inc., as producers, investigators and dis- 
tributors of essential oils, and the data resulting from more than one hundred 


years of research by scientists all over the world, as described in the technical 

The author has been most fortunate in securing the collaboration of a 
number of outstanding organic chemists, specialists in the chemistry and 
analysis of essential oils. Their valuable contributions have enabled him 
to carry the first part of this work far beyond his original conception. 

It is the plan of this first volume to describe, from a general point of 
view, the history, chemistry, biological origin and functions of the essential 
oils, method of production and analysis. The second volume will deal with 
the chemical constituents of essential oils. Succeeding volumes will be 
devoted to individual oils, their botanical and geographical origin, specific 
methods of production, physicochemical properties, assay and use. 

The completion of this series represents the culmination of a life's work. 
Much painstaking toil has gone into it. It is an attempt to present basic 
facts in the science of esvsential oils, so far as these arc now known. May it 
be received as a modest effort toward that end. 

New York, N. Y. 
September, 194? 


A thorough treatise on essential oils must of necessity include some 
discussion of the ancillary sciences of botany, biochemistry, organic and 
analytical chemistry, and pharmacology to mention only a few. It would, 
therefore, l>e impossible for a single individual to write a reliable and com- 
plete account of essential oils without the assistance of experts in associated 

The author has made use of such assistance, and takes this opportunity 
to thank those who have worked so hard and so long with him on a difficult 

Dr. A. J. Haagen-vSmit for his chapter, "The Chemistry, Origin and 
Function of Essential Oils in Plant Life." 

Mr. Edward E. Langenau for his chapter/ 'The Examination and Anal- 
ysis of Essential Oils, Synthetics, and Isolates/' and for his advice on other 
phases of the work. 

Dr. George Urdang for his chapter, "The Origin and Development of 
the Essential Oil Industry. '' 

The late Dr. Philip W. Schutz, Professor of Chemistry, University of 
California, Berkeley, California, for his help with the chapter on "Dis- 
tillation. 1 ' 

Dr. Darrell Althausen, Manager of Fritzsche Brothers, Inc., Clifton 
Factory, for his valuable suggestions on the entire manuscript. 

Mr. Carl J. Kwnig of Fritzsche Brothers, Inc., Clifton Factory, for his 
jussistance with the drawings in the chapter on "Distillation." 

Dr. Frances S. Sterrett of Fritzsche Brothers, Inc., New York, for her 
assistance with various parts of the manuscript. 

Meml>ers of the staff of Fritzsche Brothers, Inc., New York, among them 
Mr. W. P. Leidy, Chief Librarian, and Mr. Anthony Hansen, Jr., Librarian, 
for their painstaking bibliographic work; and Mrs. Ann Blake Hencken, 
Miss Catherine McGuire, Mrs. Agnes Clancy Melody and Mrs. Elizabeth 
Campbell Adelmann for their patient, diligent and exact work in transcribing 
the author's and his collaborators' very difficult and oft-revised manuscripts. 

In addition to the above, the author wishes to acknowledge most grate- 
fully help from many friends and producers throughout the world, especially 
Mr. Pierre Chauvet, Seillans (Var), France, who supplied him with a great 
deal of information about latest developments in France. 



All temperatures given in this work are expressed in degrees Centigrade 
unless otherwise specified in the text. 




by George Urdang 







PRODUCTION ... . 11 


by A, J. Haagcn-Smit 





by Ernest Gucnthcr 


Introduction 87 



a. Treatment of the Plant Material 104 

Comminution of the Plant Material 104 

Storage of the Plant Material 108 

Loss of Essential Oil in the Plant Material Prior 

to Distillation 108 

Change in the Physicochemical Properties of Es- 
sential Oils During Plant Drying 110 



b. General Methods of Distillation . ... 1 1 1 

Water Distillation 112 

Water and Steam Distillation 113 

Steam Distillation 113 

The Effort of Hydrodiffusioii in Plant Distillation 114 

The Effect of Hydrolysis in Plant Distillation ... 118 

The Effect of Heat in Plant Distillation 118 

Conclusions 110 

c. Equipment for Distillation of Aromatic Plants 1 23 

The Retort 123 

Insulation of the Retort 131 

Charging o f the Still 132 

The Condenser.. . . 132 
The Oil Separator . . .137 

Steam Boilers . . . 140 

d. Practical Problems Connected with Essential Oil 

Distillation .142 

Water Distillation ... ... 1J2 

Water and Steam Distillation . .... 147 

Steam Distillation. . 151 

End of Distillation. . . . 153 

Treatment of the Volatile Oil .153 

Treatment of the Distillation Water . . 154 

Disposal of the Spent Plant Material. . . . 150 

Trial Distillation 150 

Steam Consumption in Plant ] distillation . .159 

Rate of Distillation . 1 04 

Pressure Differential Within the Still 105 

Pressure Differential Inside and Outside of Oil 

Glands 100 

Effect of Moisture and I Feat upon the Plant Tissue 1 07 
Influence of the Distillation Method on tho 

Quality of the Volatile Oils 1(57 

General Difficulties in Distillation 108 

e. Hydrodistillation of Plant Material at High and at 

Reduced Pressure, and with Superheated Steam 168 
Steam Distillation of Plant Material at High 

Pressure 108 

Water Distillation of Plant Material at High 

Pressure 109 



Steam Distillation of Plant Material at Reduced 

Pressure J 09 

Water Distillation of Plant Material at Reduced 

Pressure 171 

Superheated Vapors J 72 

Distillation of Plant Material with Superheated 

Steam 172 

Advantages and Disadvantages of High-Pressure 

and Superheated Steam in Plant Distillation . . 173 

/. Field Distillation of Plant Material 174 

Distillation of Lavender in France 1 75 

Distillation of Pctitgrain Oil in Paraguay ... .175 

Distillation of Linaloe Wood in Mexico 170 

Distillation of Cassia Leaves and Twigs in China 170 

g. Rectification and Fractionation of Essential Oils. 178 

Rectification of Essential Oils. . . . . 179 

Fractionation of Essential Oils . . 181 

Inadequacies of Hydrodistillation .... . 185 
h. Hydrodistillation of Essential Oils at High and at 

Reduced Pressure, and with Superheated Steam 185 
Water Distillation of Essential Oils at Reduced 

Pressure 185 

Water Distillation of Essential Oils at High 

Pressure 180 

Distillation of Essential Oils with Superheated 

Steam 180 

Distillation of Essential Oils with Superheated 

Steam at Reduced Pressure 187 

It. NATURAL FLOWER OILS. ... . .... 188 


a. Preparation of the Fat Corps . ... 190 

b. Enfletirage and Dcfleitragc. . . . 191 

c. Alcoholic Ext raits . . 195 

d. Absolutes of Enflciiragc. . ... 190 
c. Absolutes of Chassis ... . ... 197 



a. Selection of the Solvent 201 

Petroleum Ether 202 




Benzene (Benzol) 203 

Alcohol 204 

b. Apparatus of Extraction . . 204 

General Arrangement . ... 204 

Construction of Apparatus . . . .... 205 

Description of Extraction Batteries. ... . 206 

Rotatory Extractors 208 

Concentration of Solutions 209 

Final Concentration . . . 210 

Concrete Flower Oils . 210 

Conversion of Concretes into Absolutes. . .211 

Conclusions . 212 

c. The Evaluation of Natural Flower Oils and Res- 

inoids 213 




by Edward E. Langcnau 




1. Specific Gravity 230 

2. Optical Rotation ... . 241 

a. Liquids ... . . . 242 

b. Solids 243 

3. Refractive Index . . . ... 244 

4. Molecular Refraction .... 247 

5. Solubility 249 

a. Solubility in Alcohol . 249 

b. Solubility in Nonalcoholic Media 251 

6. Congealing Point 253 

7. Melting Point 254 

8. Boiling Range 256 

9. Evaporation Residue 259 

10. Flash Point 261 


1. Determination of Acids 263 



2. Determination of Esters 265 

a. Determination by Saponification with Heat 265 

b. Determination by Saponification in the Cold 271 

3. Determination of Alcohols 271 

a. Determination by Acetylation 271 

b. Determination of Primary Alcohols 275 

c. Determination of Tertiary Terpene Alcohols 27(j 

(/. Determination of Citronellol by Formylation 278 

4. Determination of Aldehydes and Ketones 27 

a. Bisulfite Method 27 

b. Neutral Sulfite Method 282 

c. Phenylhydrazine Method 284 

d. Hydroxylaminc Methods 28* 

5. Determination of Phenols 291 

6. Determination of Cineole 29^ 

7. Determination of Ascaridole 29 

8. Determination of Camphor 301 

9. Determination of Methyl Anthranilate 305 

10. Determination of Allyl Isothiocyanate . ... 30^ 

11. Determination of Hydrogen Cyanide 30- 

12. Determination of Iodine Number 30t 


1. Flavor Tests 30( 

2. Tests for Halogens 30' 

3. Tests for Heavy Metals 30< 

4. Test for Dimethyl Sulfidc in Peppermint Oils 311 

5. Tests for Impurities in Nitrobenzene 3K 

a. Test for Thiophene 31! 

b. Soap Test 31! 

6. Test for Phellandrene . .. . 31! 

7. Test for Furfural 3U 

8. Test for Phenol in Methyl Salieylate 3\, 

9. Determination of Essential Oil Content of Plant Material 

and Oleoresins 31' 

10. Determination of Ethyl Alcohol Content of Tinctures and 

Essences 31' 

11. Determination of Water Content 32i 

a. Determination by the Bidwell-Sterling Method .... 32 

b. Determination by the Karl Fischer Method 32 

12. Determination of Stearoptene Content of Rose Oils 32 

13. Determination of Safrole Content of Sassafras Oils 32 ( 



14. Determination of Cedrol Content of Cedarwood Oils .... 330 

15. Determination of the Color Value of Oleoresin Capsicum 330 

1. Detection of Foreign Oils in Sweet Birch and Wintergreen 

Oils 331 

2. Detection of Petroleum and Mineral Oil 332 

a. Oleum Test 332 

6. Schimmel Tests 332 

3. Detection of Rosin . 334 

a. Detection of Rosin in Balsams and Gums. . . 334 

6. Detection of Rosin in Cassia Oils 335 

c. Detection of Rosin in Orange Oils . 335 

4. Detection of Terpinyl Acetate . 336 

5. Detection of Turpentine Oil 337 

6. Detection of Acetins 338 

7. Detection of Ethyl Alcohol 338 

8. Detection of Methyl Alcohol 340 

9. Detection of High Boiling Esters . . . 340 

a. Detection of Various Esters . 340 

b. Detection of Phthalates .... 342 

10. Detection of Mentha Arvensis Oil 343 

11. Detection of Various Adulterants 3 13 










INDEX 415 



Fractionation of oil of peppermint 47 

Boiling points of straight-chain hydrocarbons 49 

Lysigenous oil sac in Kubus rosacfolius Smith 66 

Tangential section showing oil glands of Washington navel orange fruit 67 
Percentages of mint oils and their components at various stages of 

development 70 

Total oil content in growing leaf and branch of Citrus Aurantium 72 

Composition of oil from growing tips of Eucalyptus cneorifolia 74 

Vapor of ItoswarinuK officinal is on Dracocephalum moldavica 80 

Typical boiling point and vapor-liquid equilibrium diagram at constant 

pressure ... 98 

Still with fractionating column. . . 99 

Partial and total pressure curves for a mixture obeying Raoult's law. . 101 
Partial and total pressure curves for a mixture showing deviation from 

Raoult 's law 102 

Vapor-liquid equilibrium diagram at constant temperature 102 

Haschig rings 103 

Three-pair high roller mill. . . . .... . . 105 

Stainless, non-corrosive comminuting machine. . . . 107 

Typical old-fashioned lavender still as used years ago in Southern 

France 112 

Field distillery of lavender in Southern. France. 113 

Field distillation of lavender flowers in Southern France 114 

Galvanized iron retort for steam distillation. ... . ... 124 

Top view of galvanized iron retort . . 125 

Top of retort . . 127 

Hydraulic joints or water seals l>etween still top and retort. . . . . 127 

Two types of multi-tray retorts .128 

I'se of baskets for holding still charge ... . . ... 12fl 

Tilting still on tnmions . 130 

An old-fashioned zigzag condenser 133 

Coil condenser 13E 

Tubular condenser 13 

Florentine Husks 137 

Oil separator for oils lighter and/or heavier than water 13 

Oil and water separator for oils lighter and/or heavier than water. ... 13 




Still for water distillation 148 

Still for water and steam distillation . . ... 150 

Field distillation of rosemary in Tunis 151 

An experimental still . ... 158 

An experimental still with automatic cohobation .160 

An old-fashioned direct fire still as used years ago for the distillation 

of lavender in Southern France 175 

Vacuum stills . . . . 183 

Dual-purpose essential oil still . ... 184 

Enfleurage process . . 192 

Defleurage process . . 194 

Batteuse for the extraction of flower concretes with alcohol . . . 195 

Extraction of jasmine flowers with volatile solvents. . . . 20(> 

Schematic diagram of an extraction system . 207 

Rotary extractor, Gamier type 208 

Vacuum still for the final concentration of natural flower oils 210 

Vacuum still for the concentration of alcoholic washings 211 

Apparatus for the aeration of essential oils ... 233 

Pycnometer . . . . 237 

Apparatus for the determination of melting point. . .... 255 

Apparatus for the determination of boiling range . .257, 258 

Tag open cup tester for the determination of flash point 2f>2 

Saponification flask . ... . . . 2(>f> 

Acetylation flask ... 273 

Cassia flasks . . 280 

Apparatus for phenol determination . . 292 

Mustard oil flask 304 

Apparatus for the determination of dimethyl sulfido 311 

Apparatus for the detection of phenol in methyl sal icy late 31(> 

Apparatus for the determination of the volatile oil content of plant 

materials 317 

Apparatus for the determination of alcohol ... . . . 320 

Apparatus for the determination of water . 325 

Apparatus for the detection of high boiling esters 342 






Note. All temperatures in this book are given in degrees 
centigrade unless otherwise noted. 




Ex Oriente Lux "The sun rises in the East." Symbolically this old 
saying glorifies the East as the cradle of civilization. In the East also began 
the history of essential oils ; for the process of distillation the technical 
basis of the essential oil industry was conceived and first employed in the 
Orient, especially in Egypt, Persia and India. As in many other fields of 
human endeavor, it was in the Occident, however, that these first attempts 
reached their full development. If oriental meditation kindled the light, 
occidental genius and industry kept it burning! 

Data on the methods, objectives and results of distillation in ancient 
times are scarce and extremely vague. Indeed, it appears that the only 
essential oil of which the preparation (by a somewhat crude distillation) 
has been definitely established is oil of turpentine and, if we care to men- 
tion it in connection with essential oils, camphor. The great Greek historian, 
Herodotus (484-425 B.C.), as well as the Roman historian of natural history, 
Pliny (23-79), and his contemporary, Dioscorides the author of the treatise 
"De Materia Medica" which dominated therapy for more than 1,500 years 
mention oil of turpentine and give partial information about methods of 
producing it. They do not describe any other oil. 

Until the early Middle Ages (and even later) the art of distillation was 
used primarily for the preparation of distilled waters. Where this process 
resulted in a precipitation of essential oils, as in the crystallization of rose 
oil on the surface of distilled rose water, it is likely that the oil was regarded 
as an undesired by-product rather than as a new and welcome one. 

An extensive trade in odoriferous oils and ointments was carried on hi 
the ancient countries of the Orient and in ancient Greece and Rome. 1 The 
oils used, however, were not essential oils, nor were they produced by mixing 
the latter with fatty oils; they were obtained by placing flowers, roots, etc., 
into a fatty oil of best quality, submitting the glass bottles containing these 
mixtures to the warming influence of the sun and, finally, separating the 

1 Urdang, "Pharmacy in Ancient Greece and Rome," Am. J. Pharm. Educ. 7 (1943), 169. 



odoriferous oil from the solid constituents. Sometimes the flowers, etc., 
were macerated with wine before the fatty oil was added, and the product 
obtained by digestion filtered and then boiled down to honey consistency. 

The same way of preparing odoriferous oils is described in the "Grabad- 
din" written by the somewhat mysterious Joannes Mesue, and published 
probably in the middle of the thirteenth century. This very widely used 
book did not list a single essential oil. However, two oils prepared by de- 
structive distillation (oil of juniper wood or cade, and oil of asphaltum) are 

The first authentic description of the distillation of real essential oils 
has been generally ascribed to the Catalan physician, Arnald cle Villanova 
(1235(?)-1311) who, by including products of distillation other than oil of 
turpentine, may be said to have introduced tho art of distillation into 
recognized European therapy. However, it is by no moans certain whether 
the "distilled" oils of rosemary and sage listed in tho 1505 Venetian odition 
of his "Opera Omnia" were really mentioned in the original manuscript 
(written about two hundred years earlier) or were intorpolatod at some lator 
time. Furthermore, it should be kept in mind that the term "distilled" in 
ancient and medieval writings did not have the exclusive and particular 
meaning it has today. It was, as E. Kremers pointed out in his translation 
of Fr. Hoffmann's historical introduction to E. Gildemeister and Fr. Hoff- 
mann's "The Volatile Oils," 2 "a collective term, implying the preparation of 
vegetable and animal extracts according to the rules of the art, or rectifica- 
tion and separation." 

Nevertheless, whether Arnald de Villanova actually had prepared real 
distilled oils or not, his praise of the remedial qualities of distillod waters 
resulted in the process of distillation becoming a specialty of medieval and 
post-medieval European pharmacies a specialty artfully executed and 
subjected to practical research, as well as to the theories of the time. Dis- 
tillation being a means of separating the essential from the crude and non- 
essential with the help of fire, it met in an almost ideal way the definition 
of a "chymical" process valid until about the end of the seventeenth century 
and given a special meaning by the great Swiss medical reformer, Bombastus 
Paracelsus von Hohenheim (1493-1541). His theory was that it is the last 
possible and most sublime extractive, the Quinta essentia (quintessence) 
which represents the efficient part of every drug, and that the isolation of this 
extractive should be the goal of pharmacy. This theory undoubtedly laid 
the basis for research in the preparation of essential oils after his time. 
The very name "essential" oils recalls the Paracelsian concept the Quinta 

* Milwaukee (1900), 22. 



There is still other evidence that the production and use of essential 
oils did not become general until the second half of the sixteenth century. 
In 1500 and 1507, there appeared at Strassburg the two volumes of Hierony- 
mus Brunsch wig's famous book on distillation, " Liber De Arte Distillandi." 
The author (1450-1534) was a physician at Strassburg. Although ob- 
viously endeavoring to cover the entire field of distillation techniques and 
products, he mentions only four essential oils, namely, the oil of turpentine 
(known since antiquity), oil of juniper wood and oils of rosemary and spike. 
Brunschwig states that oil of spike is produced in "Provinz," meaning un- 
doubtedly the French Provence. This is confirmed in the "New Gross 
Pe.stillirbuch" of the Strassburg physician, Walter Reiff (Ryff), published 
in 1550 at Frankfort on the Alain, and containing a reference to a French 
industry of essential oils, especially of oil of spike. "The oil of spike or 
lavender/' writes Reiff, "is commonly brought to us from the French Prov- 
ence, filled into small bottles and sold at a high price" ("gemeyncklichausder 
Provinz Frankrcich zu uns gebracht wird, in kleine Gldsslin eingefasst und 

In the part of the book dealing with the appropriate preparation of 
"some exquisite oils" by means of artificial distillation ("von rcchter Bereytung 
kiinstlichcr Dextillation etlicher furnehmer O/e j "), Reiff mentions, as sources of 
"precious" oils, clove, mace, nutmeg, anise, spike and cinnamon, as well as 
many substances that do not contain essential oils, or furnish only 
traces of them, such as benzoin, sandarac and saffron. The method as de- 
scribed by him, moreover, was by no means apt to produce pure essential oils. 

It was the" Kriiuterbuch" of Adam Lonicer (1528-1586), the first edition 
of which appeared at Frankfort on the Main in 1551, which may be regarded 
as a significant turning point in the understanding of the nature and the 
importance of essential oils. Lonicer stresses the medicinal value of "many 
marvelous and efficient oils of spices and seeds" ("vid herrlichc und krdfftigc 
Ohle von Gcwurzcn und Samen") and states that "the art of distillation Ls 
quite a recent, not an ancient invention, unknown to the old Greek and Latin 
physicians, and indeed has not been in use at all" ("Diese Kunst des Destil- 
lirens ist fast eine neuc, und nicM gar altc Erfituiung, den alien griechischen 
und latcinisehen Medicis unbekannt und gar nicht in gebrauch geiucscn"). 

Further progress in the methods of preparation and the knowledge of the 
nature of essential oils was made obvious in the "De Artificiosis Extrac- 
tionibus" written by the German physician, Valerius Cordus (1515-1544), 
and published in 1561 at Strassburg by the Swiss naturalist, Conrad Gtesner 
(1516-1565). It is significant that Cordus based his reports on the experi- 
ments conducted by him in the pharmacy of his uncle, Johannes Raila, 


apothecary in Leipzig, by whom his work was supervised. Gesner himself 
contributed to the progress in the "Thesaurus Euonymi Philiatri," a book 
published by him at Zurich under the pen name, Euonymus Philiatrus. 
The most important publication on essential oils during that period, how- 
ever, came from the pen of one of the most prolific and careful scientific 
writers of all times, the Neapolitan, Giovanni Battista della Porta (1537- 
1615). In his "De Destillatione libri IX," written about 15G3, he not 
only differentiates distinctly between expressed fatty and distilled essential 
oils, but describes their preparation, the ways of separating the volatile 
oils from water and the apparatus used for this purpose. 

In 1607, in his famous "Pharmacopoea Dogmaticorum Rostituta" 
(Frankfort on the Main), the French physician, Joseph Du Chcsne, latinized 
Quercetanus (1544-1609), one of the most ardent Paracelsians, could already 
state that "the preparation of essential oils Is well known to everybody, even 
to the apprentices" ("pracparatio omnibus fere, imo ipsis tynmibiift, nola et 
perspecta est"). z Quercetanus states that all the pracparationcs chymicac, 
among which were included the essential oils, could be obtained in the phar- 
macies, and he gives enthusiastic praise to the manager of the court phar- 
macy at Cassel in saying that it was primarily the example set in this 
pharmacy which inspired parts of his book (^Officina haccmihitypusprirnux 
fuit, ad cuius imitationem meam phannacopcam cenatus sum"). 4 As to the 
preservation of essential oils in the pharmacies, Quercetanus writes that 
"15 or 20 different oils were kept in small round boxes and, when asked for, 
they were delivered by means of a toothpick, i.e., in a minute quantity 
achieving, nevertheless, the best results" ("Eiusmodi csscntine conservantur 
in parvis theculis rotundis, quarum singulae capiunt 15 vcl 20 diver sa csscn- 
tiarum genera, quae, cum u&us postulat, cum dentiscalpio, hoc cst, in minima 
quantitate exhibebuntur, et eff edits nihilominus profercnt optatissimos") . 5 

Official pharmacopoeias have always been more or less conservative. 
Thus, only such drugs as had found general acceptance in contemporary 
medical science were given a place in these official pharmaceutical standards. 
Hence, it is not quite as surprising as it may seem at first sight that, in the 
"Dispensatorium Pharmacopolarum" of Valerius Cordus (published and 
made official in the Imperial city of Nuremburg in 1546), only three essential 
oils were listed, in spite of the author's own extensive study of them. These 
were: oil of turpentine, oils of spike (lavender) and of juniper berries, in 
general use at least since the end of the fifteenth century. Of interest is 
the reference to an industry of essential oils, which makes it practicable to 
buy the oils of juniper berries and of spike, rather than to prepare them in the 

8 P. 245. 

4 P. 246. 

5 P. 246. 


laboratories of the pharmacies. As to the oil of juniper berries, the Dispen- 
satorium does not give an explicit formula, because, as it states, the product 
is bought at a price lower than the cost of preparation by the individual 
pharmacist ("quid vero minoris emitur, quam ut ab aliquo pharmacopoea 
praeparari qucat, confectionem cius non indicaminus") .* The section dealing 
with oil of spike states that it is more advantageous to buy the oil from 
merchants who import it from France and names Narbonne as the seat of 
the industry ("apud non maioribus sumptibus fit quam in Gallia Narbonensi, 
idco potius emend urn cat a mcrcatoribus qui illud e Gallia afferunt"). 1 The 
second official Xuremburg edition of the "Dispensatorium Valerii Cordi," 
issued in 1592, lists not less than 61 distilled essential oils, 8 which fact illus- 
trates the rapid development of the knowledge of essential oils as well as 
official acceptance. 

In the seventeenth and eighteenth centuries, it was chiefly the pharma- 
cists who improved methods of distillation and made valuable investigations 
into the nature of essential oils. Of special importance was the work of 
the French apothecaries, M. C haras (1018-1698), N. Lemery (1645-1715), 
A. J. GeofTroy (1(585-1752), G. Fr. Rouelle (1703-1770), J. F. Demachy 
(1728-1803), and A. Haum6 (1728-1804); their German colleagues, Kaspar 
Neumann (1683-1737), J. Ch. Wiegleb (1732-1800), and F. A. C. Gren 
(1760-1798); and the German-Russian pharmacist, J. J. Bindheim (1750- 
1825). Of other investigators of this period, we may mention two famous 
physicians, the Dutch, II. Boerhave (1668-1738) and the German, Fr. 
Hoffmann (1660-1743); and finally the man regarded as one of the first 
great industrial chemists, the Gorman, J. R. Glauber (1604-1670). 


The revolution in the science of chemistry, which began at the end of the 
eighteenth century with the work of A. Lavoisier (1743-1794), resulted in 
a new and illuminating approach to the investigation of the nature of es- 
sential oils. It is of interest that the first really important modern investi- 
gation in the field was devoted to the oldest essential oil known, oil of tur- 
pentine. Submitting the oil to elementary analysis, J. J. Houton de la 
Billardiere found the ratio of carbon to hydrogen to be five to eight the 
same ratio that was later established for all hemiterpenes, terpenes, sesqui- 
terpenes and polyterpenes. The investigator published his results in a 
pharmaceutical periodical, the Journal dc Pharmacic (4 [1818], 5). 

The systematic study of essential oils may be said to have begun with 
the analysis of a number of stearoptenes by the great French chemist, J. B. 

"Dispensatorium Pharmacopolarum Valerii Cordi," Norimbergae, 1546, col. 220. 

T /Wtf., col. 241. 

8 Wi ikler, "Das Dispensatorium des Valerius Cordus," Mittenwald, 1934, 11. 


Dumas (1800-1884), who had started his career as a pharmacist. He pub- 
lished his first treatise devoted to essential oils in Licbig's Annalen der 
Pharmacie (6 [1833], 245). 

Of considerable importance in the further development of the chemistry 
of volatile oils were the investigations of the French chemist, M. Berthelot 
(1827-1907), devoted primarily to the hydrocarbons contained in these 
oils. About 1866 the name Terpene was mentioned in a textbook written 
by Fr. A. Kekul6 (1829-1896) who apparently coined this term. In 1875 
one of the greatest English chemists emerging from pharmacy, W. Tilden 
(1842-1926), introduced nitrosyl chloride as a reagent for terpenes, a reac- 
tion perfected and used to such an extent and with such excellent results 
by the German chemist, O. Wallach (1847-1931), that the renowned Swiss 
pharmacognosist, Fr. A. Fliickiger (1828-1894), called Wallach the Messiah 
of the terpenes. 

This very active and far-reaching research was the result, as well as the 
cause, of the wide expansion in the use of essential oils during the latter half 
of the nineteenth century; and it is difficult to decide which ranks first, 
the result or the cause. Gradually the use of essential oils in medicinal 
drugs became quite subordinate to their employment in the production of 
perfumes, beverages, foodstuffs, etc. The work of O. Wallach and his pupils, 
and of F. W. Semmler (1860-1931) and collaborators, on terpenes and ter- 
pene derivatives introduced what might properly be called the "Elizal>ethan 
Age" of the essential oil industry. Discovery followed discovery ; one essen- 
tial oil after the other was thoroughly investigated and its composition 
elucidated. Newly identified constituents were synthesized, and many of 
them manufactured commercially. Our industry of synthetic and isolated 
aromatics had its origin mainly in the work of these great explorers. Illus- 
trious names, such as 0. Aschan, E. Gildemeistcr, H. Walbaum, S. Bertram, 
A. Hesse, C. Kleber, E. Kremers, H. Barbier, L. Bouveault and E. Charabot, 
etc., are connected with these classical investigations, which are still being 
carried on with ever greater results by some of our greatest contemporary 
scientists, including L. Ruzicka in Zurich arid J. L. Simonsen in London, not 
to mention other diligent workers in the United States, in the British Com- 
monwealth, the U.S.S.R., Switzerland, France, Germany and in the Far 
East. It should be emphasized in this connection that Wallach's work also 
laid the foundation for another important chapter in the chemistry of es- 
sential oils, viz., the analysis or assay of products which, because of their high 
price, are prone to fraudulent manipulation and adulteration by unscrupu- 
ous producers or dealers. 



It appears that almost every important discovery in the history of the 
essential oils is connected with the oil of turpentine. The first large-scale 
production of an essential oil in the United States of America was that of 
oil of turpentine. There were, naturally, good reasons for this fact: the 
enormous areas covered by pine forests, especially in North and South 
Carolina, Georgia and Alabama, and the great and steadily growing demand 
for the oil at home, as well as abroad. 

Although tar, pitch and common turpentine (the oleoresin) were men- 
tioned as products of Virginia in official reports as early as 1610 (D. Han- 
bury in Proc. Am. Pharm. Assocn. 19 [1871], 491), the production of oil 
of turpentine in North Carolina and Virginia seems not to have started until 
the second half of the eighteenth century. One of the earliest authentic 
reports on the production of oil of turpentine in Carolina was given by the 
German physician and explorer, J. D. Schopf, in his book entitled "Reise 
durch einigo dor mittleren und sudlichen Vereinigten Nordamerikanischen 
Staaten in don Jahrcn 1783 und 1784," (Erlangen 1788, Vol. 2, 141, 247-252). 

In the early nineteenth century, the production of other essential oils 
was started in the I'nited States and it is generally assumed that the oils 
of three indigenous American plants, of sassafras, of American wormseed 
(Chcnopodinm anthclmtnticum L.) and of wintergreen (a closely related and 
similar oil can be obtained from the bark of sweet birch) were, in addition 
to oil of turpentine, the first oils to be produced in the United States 
of America. The oils of wintergreen and American wormseed have always 
boon hold in especially high esteem on the North American continent. It 
was by their introduction into the first ''United States Pharmacopoeia," 
published in 1820, that, for the first time, both oils were given official 

Of oil of wintergreen, Jacob Bigelow tells in his "American Medical 
Botany" (Boston 1818, Vol. 2, 31) that it is "kept for use in the apothecaries 1 
shops." No loss a person than the apothecary, William Proctor, Jr. 
called "The Father of American Pharmacy" identified the principal consti- 
tuents of the oils from wintergreen (Gaulthcria procumbcns L.) and from the 
bark of sweet birch (Hctula Icnta L.) already hinted at by Bigelow. The use 
of wintergreen oil for medicinal, cosmetic and flavor purposes has been 
nowhere so popular as in the United States, and yet there is no evidence 
whatsoever of a production of wintergreen oil on a commercial scale before 
or until shortly after 1800. 

The same holds true as to the essential oil of American wormseed. Ben- 
jamin Smith Barton mentions the wormseed plant in his "Collections for an 
Essay Towards a Matcria Medica of the United States" (Philadelphia, 1798, 


40 and 49) in the rubric "Anthelmintics." He states that "it is the seeds 
that are used" and does not mention the oil. James Thatcher in "The Amer- 
ican New Dispensatory" (Boston, 1810, 99) tells that "the whole plant may 
be employed" as an anthelmintic, and that "sometimes the expressed juice 
is used." In general, however, the seeds "are reduced to a fine powder, 
and made into an electuary with syrup." He repeats the same statement in 
the second and third editions of his book (1813 and 1817) ; and it was not 
until 1821, i.e., after the issuance of the U.S. P. 1820 listing Oleum cheno- 
podii, that Thatcher, in the fourth edition of his dispensatory (pp. 173-174), 
added to the above cited text the following passage: "The essential oil of 
chenopodium or wormseed is found to be one of the most efficacious vermi- 
fuge medicines ever employed." Any large-scale production of American 
wormseed oil had in all probability not taken place before the twenties or 
even thirties of the nineteenth century. In the course of a controversy 
concerning the quality of the oil prepared from plants grown in Maryland 
and in "the western states" about 1850, we are told that "about twenty or 
thirty miles north of Baltimore, some fifty or sixty persons grow the plant 
in small or large patches on their land" for the production of essential oil 
(Am. J. Pharm. 22 [1850], 303). 

Apparently there existed on the North American continent a large-scale 
production of oil of peppermint prior to any remarkable American prepara- 
tion of the other essential oils mentioned. Until quite recently it was 
generally assumed that the distillation of American peppermint oil on a 
commercial scale had its origin in Wayne County, New York, in 1816. 
We know now that such an industry must have been in existence at least 
as early as 1800. In the booklet "150 Years Service to American Health," 
published by Schieffelin and Company, New York, in 1944, we are told of 
an offer of "homemade oil of peppermint" made by "Dr. Caleb Hyde, 
Physician and Druggist, Lenox, Berkshire, Mass." to Jacob Schieffelin, in 
1805. The addressee answered as follows : 

"The oils of peppermint and common mint has (sic) in conse- 
quence of the large quantities made in the United States become 
a mere drug in our market and no sale for it I have exported a 
quantity it has lain for years in England without a purchaser 
and I shall eventually become a loser thereby." 

The oils of turpentine and of peppermint were not only the first essential 
oils to be produced on a commercial scale in the United States but they have 
been up to the present among those that rank first in the quantity produced. 
Others, such as oil of orange, lemon, grapefruit, etc., will be described else- 
where in this \vbrk. 



Developed, in the course of centuries, from obscure beginnings into an 
important modern industry, the present-day production of essential oils 
Ls based upon principles which vary between two extremes (the first still 
retaining its original primitive character). 

(1) In most instances the aromatic plants grow wild or are cultivated as 
garden or patch crops by natives of the area concerned. Cultivation of the 
plants and distillation of the oil represent a family industry often, indeed, 
only a "side occupation" of members of the family. By primitive methods, 
and limiting themselves generally to one oil, the natives produce small 
quantities of an oil, which they sell through field brokers to village buyers, 
until the lots finally reach exporters in the shipping ports. The price of 
these oils depends upon the market, which, in turn, is influenced by supply 
and demand. The natives are usually well aware of prevailing quotations, 
and prefer stocking up their output to selling it at unattractive prices. This 
primitive industry is at a very definite advantage because the native oper- 
ators never value very highly the work done by themselves or their 
families, while modern methods of production involve specialized and highly 
priced labor. 

This old-fashioned method of essential oil production is characterized 
by dispersion rather than by concentration. Lack of roads prevents trans- 
port of the plant material to centrally located processing plants. The stills, 
usually small, portable contraptions, low priced and easy to operate, have 
to be scattered over the regions concerned, thus following the plant material. 
Such conditions still exist with respect to numerous oils and in many parts 
of the world, for example in East India (oil of lemongrass, palmarosa, etc.), 
in China (oil of star anise, cassia), and in Java (oil of cananga), etc. 

(2) Advanced processing methods, based upon modern principles of 
plant breeding, mechanized agriculture, engineering and mass production, 
represent the competing counterpart of the primitive methods described 
above. The oils obtained in regular essential oil factories generally possess 
a quality superior to those produced by natives in backward districts; but 
the operating expenses are high. In addition to the higher standard of 
living and consequent higher wages and salaries involved, the amortization 
of invested capital, taxes and other general overhead expenses increase the 
costs of production. Under these conditions, a modern factory trying to 

This part of the survey leans on writings by Ernest Guenther, "Essential Oil Produc- 
tion in Latin America," in "Plants and Plant Science in Latin America," p. 205, by Frans 
Verdoorn, Waltham, Mass., 1945; "Essential Oils and their Production in the Western 
Hemisphere," New York, 1942, Fritzsche Brothers, Inc.; and "A Fifteen Year Study of 
Essential Oil Production Throughout the World," New York, 1940, Fritzsche Brothers, Inc. 


specialize in the production of only one yearly crop could hardly survive ; 
operation is profitable only if a variety of plants can be processed and thereby 
the enterprise kept busy during most of the year. Such an organization 
would have to produce oils from plants grown mainly in the vicinity, or 
from dried plants which could be shipped from afar at low cost. In other 
words, a factory of this type would have to be located near large plantations, 
connected by good roads, and would require conditions of soil, climate and 
altitude permitting the growth of varied crops of aromatic plants. Theo- 
retically, this would offer the ideal solution for the essential oil industry, but 
it involves heavy capital investment and necessitates a great deal of ex- 
perience and lengthy, systematic agricultural research work before the 
proper location can be found and the proper crops selected and grown. 
Highly mechanized farming equipment (bulldozers, tractors, planting, cul- 
tivating and harvesting machinery, trucks, etc.) must be employed in order 
to reduce the high cost of American labor (labor is a much smaller item in the 
"cost calculation" of the native patch croppers abroad). Furthermore, 
scientific plant breeding would have to aim at strains with a high oil yield. 

Only in a few instances has the production of essential oils been placed 
on a really modern agricultural and technical basis. Previous to World 
War I, the great essential oil factories in and near New York City, London, 
Leipzig, and Grasse (Southern France) used to distill essential oils (oils of 
sandal wood, vetiver, patchouly, etc.) from plant material imported from 
abroad. The problem of shipping space for bulky raw material which arose 
during the war forced local growers in various countries abroad to install 
their own distillation equipment and to process their own plant material 
for oil. As a result, after World War I, the high cost of transporting raw 
material prevented manufacturers in Europe and the United States from 
competing with native producers abroad. Hence the production of essen- 
tial oils in many instances reverted from a centralized and highly developed 
system to a primitive and scattered one. 

Today only a few essential oils are produced by very modern or "cen- 
tralized" methods. Among these are the natural flower oils in the Grasse 
region of Southern France, and the citrus oils of California and Florida. 
The latter states have succeeded in producing large quantities of high quality 
oils because they possess a network of good roads and railroads permitting 
the trucking or hauling of fruit from distant orchards and sections to cen- 
trally located, modern processing plants. Because of this feature, the 
United States has become a large producer and exporter of these oils. In 
fact, it has achieved independence as regards oils of lemon and orange. 
In the coming years, a corresponding evolution may take place also in other 
oils which so far have been distilled in far-off corners of more primitive 
countries. However, although most essential oils are still imported from 


regions abroad, where old methods prevail, the American essential oil 
industry has reached a high standard because of field work carried out 
abroad and untiring analytical work in the laboratories of private firms and 
scientific institutions. 

The essential oil industry in its present stage is not limited to the produc- 
tion and distribution of essential oils and the improvement of methods, nor 
to the establishment and maintenance of standards of quality alone, but 
has come more and more to be concerned with the development, production 
and testing of synthetic aromatics and mixtures which today find their way 
into so many products of our advanced civilization. 

Botany, agriculture, pharmacy and chemistry, engineering, a knowledge 
of world markets, commercial ingenuity and responsibility have all con- 
tributed to the development of the modern industry of essential oils. It is 
the maintenance of this combination which will keep up the high standard 
and the general usefulness of this industry. 





Note. All temperatures in this book are given in degrees 
centigrade unless otherwise noted. 




Early in his history, man evinced a great deal of interest in the preserva- 
tion of the fragrant exhalation of plants, and those who were later to be 
called chemists occupied themselves with separating the essence of the 
perishable plants. It was probably observed that heating of the plant 
caused the odoriferous principle to evaporate and that upon condensation 
and subsequent cooling, droplets united and formed a liquid consisting of 
two layers water and oil. While, in such primitive experiments, the water 
from the plant is used to carry over the oils, additional water or steam was 
later introduced in "stills" to obtain better yields and quality. 

In early work, therefore, we find the term "essential oil" or "ethereal oil" 
defined as the volatile oil obtained by the steam distillation of plants. 
With such a definition, it is clearly intended to make a distinction between 
the fatty oils and the oils which are easily volatile. Their volatility and 
plant origin are the characteristic properties of these oils, and it is for this 
reason more satisfactory to include in our definition volatile plant oils ob- 
tained by other means than by direct steam distillation. 1 - 2 Bitter almond 
and mustard oil, obtained by enzymatic action, followed by steam distilla- 
tion ; lemon and orange oil isolated by simple pressing, and certain volatile 
oils obtained by extraction are, therefore, included among the essential oils. 

In the early stages of development of organic chemistry, the chemical 
investigation of oils was limited to the distillation of a great number of 
plants, and the oils which were obtained in this way were used to compose 
perfumes according to recipes, some of which are still used at the present 
time; e.g., the can de Cologne prepared in 1725 by Johann Maria Farina in 

Gradually with the advance of science came improvements in the 
methods of preparing the oils, and parallel with this development a better 
knowledge of the constituents of the oils was gained. It was found that the 
oils contain chiefly liquid and more or less volatile compounds of many 

1 Thomas, "Xthcrische Ole," in Klein, "Handbuch der Pflawenanalyse" Vol. Ill, 1 
(1932), 454. 

2 Rosenthaler, Pharm. Ada Helv. 10 (1944), 213. 



classes of organic substances. Thus, we find acyclic and isocyclic hydro- 
carbons and their oxygenated derivatives. Some of the compounds contain 
nitrogen and sulfur. Although a list of all the known oil components would 
include a variety of chemically unrelated compounds, it is possible to classify 
a large number of these into four main groups, which are characteristic of the 
majority of the essential oils, i.e. : 

1. Terpenes, related to isoprene or isopentene; 

2. Straight-chain compounds, not containing any side branches ; 

3. Benzene derivatives ; 

4. Miscellaneous. 

Representatives of this last group are incidental and often rather specific 
for a few species (or genera) and they contain compounds other than those 
belonging to the three first groups (Fig. 2.1). 

allyl isothiocyanate 

diallyl sulfide 

sec.-butyl propenyl disulfide 

CH2=CH CH 2 

CH2=CH CH 2 S CH 2 CH=CH 2 


CH 3 

CHr CH 2 CH 2 CH 2 SH n-butyl mercaptan 

CH, CH=CH CH 2 S CHs CH= CH CH 3 dicrotyl sulfide 







/ \ / 



methyl anthranllato 


FIG. 2.1. Natural occurring volatile Sulfur and Nitrogen containing compounds. 

For example, the mustard oils, containing allyl isothiocyanate, are found 
in the family of the Cruciferae ; allyl sulfides in the oil of garlic. The oil 
from Ferula asafoetida L., belonging to the family of the Umbelliferae, gained 
reputation from its active component, secondary butyl propenyl disulfide, 3 a 

* Mannich and FVesenius, Arch. Pharm. 274 (1936), 461. 


competitor of the odoriferous principles of the skunk, primary n-butyl mer- 
captan and dicrotyl sulfide. 4 The more pleasant smelling orange blossom 
and jasmine perfume betrays the presence of small amounts of anthrani- 
lates and indole, both compounds related to the amino acid, tryptophane. 

Although it is possible to list a considerable number of such singular cases, 
the most characteristic group present in many essential oils contains hydro- 
carbons, as a rule of the formula CioHie and a group of oxygen-containing 
compounds with the empirical formula doHi 6 O and Ci Hi 8 O. The classical 
book of Wallach indicates the names of these two types of compounds in its 
title "Terpene und Campher." The English word "terpene" and the Ger- 
man "Terpen" are derived from the German word "Terpentin," English 
"turpentine" and French "trebenthine." The name "Terpen" is com- 
monly attributed to Klkule*, who is said to have introduced it as a generic 
term for hydrocarbons CioHie to take the place of such words as Terebene, 
Camphene, etc. 5 - 6 The name "camphor" formerly was used to indicate the 
crystalline oxygen compounds, such as thyme camphor (C. Neumann, 1719) 
and peppermint camphor (Gaubius, 1770) ; these are now known respec- 
tively as thymol and menthol. The name "camphor" is at present limited 
to a specific compound and its more general meaning, covering the oxygen- 
ated derivatives, has been taken over by the term "terpene." With an 
increase in our knowledge, this broadened definition in its turn became too 
narrow and had to be modified to cover new and more distantly related 
compounds. Not all terpenes are represented by the formula C 5 H 8 ; there 
exist compounds which contain less hydrogen, still others which are more 
saturated. We also find terpenes, like santene (CgH^), which have only 
9 carbon atoms. The close resemblance to and probable connection with 
the Cio compounds through the terpene acid, santalic acid, make it imprac- 
tical to omit such a compound from the terpene literature. 

At the present time, therefore, we use the term terpene both in its broadest 
sense to designate all compounds which have a distinct architectural and 
chemical relation to the simple CJIs molecule, and in a more restricted sense 
to designate compounds with 10 carbon atoms derived from Ci Hi 6 . When 
confusion with the general designation is possible, members of the Cio 
group are often referred to as monoterpencs. Compounds having a more 
distant connection with the terpenes, but still containing features which 
link them with terpene structures, are sometimes called terpenoids or iso- 

4 Stevens, J. Am. Chem. Soc. 67 (1945), 407. 

Gildemeister and Hoffmann, "Die Atherischen Ole," 2cl Ed., Vol. I (1910), 90. 
6 Kremers and collaborators, "Phytochemical Terminology," J. Ain. Pharm. Assocn. 
22 (1033), 227. 


prenoids in analogy with the term steroids, which includes not only sterols, 
but many more remotely connected relatives. 7 ' 8 - 9 ' 10 

Characteristic for many of these oil constituents is their instability and 
the ease with which intramolecular rearrangements occur. These properties 
have been a great hindrance to the study of these compounds. Another 
drawback in the analysis of these oils is that most of the compounds are 
liquids so that thorough fractionation is necessary to separate the consti- 
tuents which boil within a restricted temperature range. Since in the early 
stages of research it was difficult to define sharply the isolated fraction, a 
great number of terpenes were named after the plant from which they were 

Order was brought into this chaos by Wallach, who saw clearly that the 
first task in the study of the oils was the identification of the terpenes with 
the help of crystalline derivatives, this being the only practical way we 
possess at present to identify chemical substances with certainty. Based on 
Wallach's investigation, about 500 compounds have since been isolated and 
characterized in the essential oils. After a general idea was obtained of the 
great number of distinct chemical compounds in oils, Wallach started the 
second part of his working program, i.e., studies of the relationship between 
the terpenes and the camphors. By reason of their fundamental nature and 
the clear presentation of the problems they involved, these studies provided 
great stimulus not only to his contemporaries Semmler, Harries, Tilden 
and others but had a pronounced influence on the development of chem- 
istry as a whole. The establishment of the constitution and the relationship 
of the terpenes revealed a certain regularity in their structures. As early 
as 1869 Berthelot had discovered how the hydrocarbons CioHie, Ci JI 2 4, and 
C 2 oH 3 2 are related to the hydrocarbon isoprene (C 6 H 8 ) isolated by Wil- 
liams 11 ' 12 a few years before. However, it was through the combined work 
of the aforementioned investigators that this hypothesis was established 
on a firm basis. 

The compounds which we find in the monoterpene series can be figura- 
tively divided into 2 isopentene chains; such a hypothetical combination 
gives substances of the empirical formula Ci Hi 6 . If three of these iso- 
pentene units can be recognized in the molecule, the name sesquiterpene is 
given. In the course of time there have been added diterpenes derived from 
C2oHs2, triterpenes, C 3 oH 4 8, and tetraterpenes, C4oH 6 4, and finally poly- 
terpenes with an indefinitely large number of these units (Fig. 2.2). 

7 Kremers, ibid. 

8 Gildemeister and Hoffmann, "Die Xtherischen Ole," 3d Ed., Vol. I, 15. 

9 Ruzicka, Ann. Review Biochem. I (1932), 581. 

10 Fieser and Fieser, "Organic Chemistry," Heath Co. (1944). 

11 Kremers and collaborators, "Phytochemical Terminology, " /. Am. Pharm. Assocn. 
22 (1933), 227. 

12 Williams, Jahresber. (1860), 495. 

















1 | 





1 58 

































" T 









o o 








. .-I.... 

o o 



1 1 


O O 



A - 



o o o ~ 


O v 













o o 





o - o o o 

u o 




..V 9... 





....].... ....1.... 




o o 












Q ^) Q O 

o o 






A saturated acyclic hydrocarbon with 10 carbon atoms would have the 
formula Ci H 2 2, possessing 6 II atoms more than a compound CioHie. This 
lower hydrogen content may be caused by the occurrence of double bonds, 
by ring structure, or by both, giving rise to acyclic, monocyclic and bicyclic 
representatives, with 3, 2 and 1 double bond, respectively. We have, 
therefore, the following possibilities for a molecule with the formula 
(monoterpene) : 

Acyclic No ring 

Monocyclic One ring 

Bicyclic Two rings 

Tri cyclic Three rings 

3 double bonds 
2 double bonds 
1 double bond 
No double bonds 

All these structural variations of the same empirical formula are found 
in the constituents of volatile plant oils. A chemical shorthand, developed 
by terpene chemists, has been introduced to show more clearly the principal 
structural details. This greatly simplified way of writing formulas consists 
in assuming a carbon atom at a place where valency lines end, or form an 
angle. As many C's and H's as feasible are omitted and only double bonds 
and substituents, such as hydroxyl and amino groups, are written in full 
(Fig. 2.3). Others prefer to indicate all end groups such as methyl and 
methylene groups in full. 










H,C CH, 



H S C CH, 

I I 

H.C /CH 



H,C CH, 



FIG. 2.3. Abbreviated formulas of Terpenes. 



As examples of the acyclic terpenes with 3 double bonds, we find ocimene 
and myrcene. In the frequently occurring acyclic alcohols geraniol and 
linalool, in the aldehydes citronellal and citral, and in dehydrogeranic acid 
we see several stages of oxidation and reduction of this type of terpene 
hydrocarbons (Fig. 2.4). Many of these compounds can be converted into 

H 2 OH 

cltronellol ocinienc 

CioHjoO CioHis 


CioH 18 



CioH ls O 



acid 1,2,3 

FIG. 2.4. Oxidation Stages of Acyclic Terpenes. 

1 Cahn, Penfold and Simonsen, J. Chem. Roc. (1031), 3134. 

2 Kuhn and HofTer, Her. 65 (1932), 651. 

'Fischer and Lovvonberg, Licbigs Ann. 494 (1032), 263. 

each other with great ease. Geraniol, the chief constituent of rose and 
geranium oil, is easily converted into the monocyclic alcohol a-terpineol, 
the chief constituent of the oil of hyacinth, and into linalool, which as 
acetate constitutes the characteristic component of lavender oil. 

Geraniols of variant origin have variant constants and odors, due to the 
presence of isomers. The double bond between carbon atoms 2 and 3 
makes the existence of cis- and Jrans-isomers possible, and the relative ease 


of ring formation permits one to distinguish between these forms, which 
have been called nerol and geraniol according to their origin. The double 
bond near the terminal carbons is another source of isomerism. Thus 
geraniol, nerol and other compounds with similar structure, such as citro- 
nellol and rhodinol, and citronellal and rhodinal, consist of varying quanti- 
ties of isomers containing the double bond, between either carbon atoms 7 
and 8, or 6 and 7, resulting in a further source of variation in the constants 
of the oil constituents (Fig. 2.5). 

!H 2 OH 





FIG. 2.5. Isomerism of Geraniol. 

Most of these compounds easily form cyclic derivatives under the in- 
fluence of acids, and the formulas are usually written intentionally in such a 
way as to indicate where the ring closure takes place. A saturated mono- 
cyclic terpene has the formula CioH 20 and is called menthane. If the com- 
pound has the empirical formula Ci Hi 6 , there must be 2 double bonds, 
since the ring occurs in the place of one of the 3 double bonds present in 
aliphatic terpenes. Such hydrocarbons are called menthadienes, and the 
method of indicating the position of the double bond given by Baeyer makes 


use of the Greek capital letter A (delta), and an index number indicating the 
carbon atom from which the double bond starts. If the double bond is in 
the side chain, then it will be necessary to indicate toward which carbon 
atom the double bond goes. This number is placed in brackets behind the 
number of the first carbon atom, as is indicated in Fig. 2.6. 13 

We find many representatives of this class of menthadienes among the 
terpene fractions in essential oils. For example, dipentene, formed by the 
polymerization of isoprene under the 
influence of acids, is such a com- 9 
pound. The official name of this com- I 

pound would be A 1 - 8(9) -menthadiene. /0\ 

Carbon atoms, indicated by an C (DC 
asterisk in Fig. 2.6 have four sub- I I 

stituents, each of different nature, \/f)/ 
and these substituents can be ar- Q 
ranged in two different ways around 
the carbon atom, thereby forming 
mirror images. These two forms ^ |J 

show similar chemical properties and A ^ W Si"^SSli diene 

have the same melting and boiling Fr 2f 

points, but differ in their behavior 

toward light. When plane polarized light is passed through this type of com- 
pound, the plane in which the light vibrates is rotated and the amount of this 
rotation is determined in a polarimeter. The two forms give a rotation of 
equal magnitude, but in opposite directions. Often equal amounts of the 
two forms crystallize together and this combination acts in many ways as a 
third isomer. These so-called "racemates" or their derivatives have melt- 
ing points, solubilities, etc., different from the two components, but do not 
show any optical rotation. 

In the A 1 - 8(9) -menthadienes all forms and mixtures of these optical iso- 
mers and racemates occur in nature. In pine needle and lemon oil we find 
a laevorotatory isomer called Z-limonene ; the d-form we find in oil of lemon 
and caraway, whereas the racemate, viz., dipentene, occurs in the oil of 

When we arrange the double bonds in a different way we can make a 
total of 32 isomers, which include possible optical antipodes and their 
racemic mixtures and cis- trans- forms. We see, therefore, that for this one 

18 It is customary to indicate a double bond from C 8 to one of the atoms 9 or 10 as A 8(9) , 
although with unsubstituted end groups no confusion could arise using the index A 8 . In 
the modern American literature the A sign is generally no longer used with monocyclic 
terpenes, but it is still employed in the nomenclature of the bicyclic terpenes and derivatives. 


type of terpene alone, a great number of possibilities exists. Some of these 
structures occur in nature, as is indicated in Fig. 2.7. 

The number of possibilities is further increased if the methyl and the 
isopropyl group occupy positions other than 1,4 on the cyclohexane ring. 
We find representatives of this structure in sylvestrene, a terpene derived 
from the commercial oil of Finns sylvestris. 

> 2,8(9) 

terplnoleue liuionene 

FIG. 2.7. Isomeric p-Menthadiencs. 

The monocyclic terpenes also occur in many stages of oxidation, and 
after we have seen the diversity in the aliphatic series, it is not surprising 
to find compounds with less and with more hydrogen than the general 
formula Ci Hi 6 requires, i.e., l-methyl-4-isopropenylbenzene Ci Hi 2 , in 
hashish oil; 14 p-cymene CioHn, in eucalyptus oil; and A 3 -menthene Ci Hi 8 , 
with only one double bond, in thyme oil (Fig. 2.8). Oxygen-containing 
derivatives (alcohols and carbonyl compounds) of these hydrocarbons also 
belong to the monocyclic terpene group, and many of these structures can 
be converted into each other by relatively simple chemical reactions 
(Fig. 2.9). 

In all these derivatives we see a so-called head-to-tail union of the 
branched Cs chains. The first discovered deviation from this structural 
scheme was looked upon with a great deal of suspicion. However, after the 
synthesis of a derivative of one of these compounds (i.e., tetrahydroar- 

14 Simonsen and Todd, /. Chan. Soc. (1942), 188. 





A 8 -mcnthenc ce.teiplnene p-cymcne 

FIG. 2.8. Oxidation stages of Monocyclic Terpenes. 



: H 

plperitenone 1<8 cuminaldehyde 

CioHuO CioH ls O 

benzole acid 1 

FIG. 2.9. Oxidation stages of Monocyclic Terpenes. 

1 Naves and Papazian, Helv. Chim. Ada 25 (1942), 984. 

J Penfold, Ramage and Simonscn, J. Chem. Soc. (1939), 1496. 

8 Malavya and Dutt, Proc. Indian Acad. Sci. 16A (1942), 157. 


temesia ketone) was achieved, there could no longer be any doubt about the 
possibility of irregular build-up in the terpene series. The formula of 
artemesia ketone can still be divided into branched C& chains, but no head- 
to-tail union is found. Recently two similar cases have become known, 
senecic acid, which occurs bound in senecio alkaloids in some Compositae, 
and lavandulol in oil of lavender, which is accompanied by the ester of the 
regularly built linalool (Fig. 2.10). 15 

CH, CH, 

I I 

Unalool H ,C C=CH-CHa-CH a -C CH=CH a 


CH, CH, 

artemesia kctonci H 2 C= CH C C CH 2 CH= CH a 

senecic acid' H,C CH=* G CHa CH-CH C=O t f I 



tarandulol 1 H,C~ C =CH CH 2 CH C = 

FIG. 2.10. 

1 Ruzicka, Reichstein and Pulver, Helv. Chim. Ada 19 (1936), 646. 

8 Manske, Can. J. Research 17B (1939), 1. Barger and Biackie, J. Chem. Soc. (1936), 743. 

'Schinz and Seidel, Helv. Chim. Ada 25 (1942), 1572. 

Still another way of connecting the two branched C 6 chains is observed 
in chrysanthemum acid which, esterified with pyrethrolone, is a part of the 
ester pyrethrin, the active component of insect powder made from Chrysan- 
themum ciner arc folium. The origin from a regular built carane-like bicyclic 
terpene through oxidation is indicated (Fig. 2.11). 

The third group of (bicyciic) monoterpenes has two rings, leaving room 
for only one double bond for a formula Ci Hi 6 . This type of structure we 
find in compounds such as carane, pinane, camphane, bornylane, isoborny- 
lane and fenchane. Through rearrangements of these different structures 

15 For a discussion on theoretically possible monoterpenc structures see: Schinz and 
Bourquin, Helv. Chim. Ada 25 (1942), 1599; and Schinz and Simon, Helv. Chim. Ada 28 
(1945), 774. 




(Fig. 2.12), other ring systems can be derived. Molecular rearrangements, 
shifting of double bonds to other places in the molecule, oxidation or de- 
hydrogenation and hydrogenation occur more or less readily, whereas treat- 
ment with acids may open these rings. 

The fourth group of (tricyclic) monoterpenes has as its only natural 
occurring representative teresantalic acid. 

Molecular rearrangements, leading to a shifting of the connections be- 
tween the carbon atoms, made the 
investigations of these compounds 
very complicated. On the other 
hand, through these many rear- 
rangements, a considerable number 
of conversions of great importance 
occur. The oxidation of a-pinene 
to camphor includes a simultaneous 
reattachment of the carbon atom 
carrying the two methyl groups 
to the carbon atom carrying one 
methyl group as indicated in Fig. 
2.13. Comparable is the conver- 
sion of a-pinene into derivatives of 
the fenchyl series, i.e., fenchyl al- 
cohol and fenchonc. A most in- 
genious application of this versa- 
tility is the complete conversion of 
Z-camphor into (/-camphor and vice 
versa by Houben and Pfankuch. 16 

The next class of terpene com- 
pounds contains three of our build- 
ing stones and its members are 
called sesquiterpenes, since they 
contain one and a half times as 
many carbon atoms as the mono- 
terpenes. Here, as in the terpene series, we can predict what type of com 
pound we might expect from their general formula, CuH^, i.e. : 

4 double bonds, no rings, aliphatic 
3 double bonds, one ring, monocyclic 
2 double bonds, two rings, bicyclic 
1 double bond, three rings, tricyclic 
double bonds, four rings, tetracyclic. 

"Ber. 64B (1931), 2719. Liebigs Ann. 501 (1933), 235; 507 (1933), 37. 

chrysanthemum dicarboxylic 

CH 3 



pyrethrolone 1 
FIG. 2.11. Pyrethrin in its 

relation to Terpcnes. 

1 Staudinger and Ruzicka, Helv. Chim. 
Acta 7 (1924), 201, 212. West, J. Chem. 
Soc. (1944), 239. 


Representatives of the first four groups are known, and here, as in the 
Cio series, we see representatives of different stages of oxidation and reduc- 
tion. We count among these some valuable perfume constituents like the 
aliphatic sesquiterpene alcohols, farnesol and nerolidol. These Cu alcohols 
have the same relation to each other as geraniol and linalool in the mono- 






teresantalic acid 


FIG. 2.12. Carbon skeletons of Bicyclic and Tricyclic Terpcnes. 

terpene series. Ruzicka has, therefore, called them the geraniol and linalool 
of the sesquiterpene group. This similarity is expressed by their intercon- 
versions and ring-closures to monocyclic sesquiterpenes of the bisabolene 
type, analogous to the formation of terpineol and dipentene in the terpene 
series (Fig. 2.14). 



By the addition of the unsaturated C 6 chain, the number of possibilities 
for secondary ring-closure has been increased, and the formation of a bi- 
cyclic sesquiterpene takes place easily. These ring-closures can often be 
effected by treatment with acids or by dehydrogenation with sulfur, 17 
selenium 18 and catalysts, such as platinum and palladium. 19 . By applying 


HO r 


oxidation ^ 



fenchjrl alcohol 


FIG. 2.13. Conversion in the Bicyclic Terpenc series. 

these methods, Ruzicka has done much of the ground work in the sesqui- 
terpene group. It has been found that three chief classes of compounds 
were formed, one belonging to the ring structure characteristic for a group 
of blue hydrocarbons sometimes found in essential oils, and two to that 
characteristic of the naphthalene group, i.e., cadalene and eudalene. Al- 
though the cadalene formation is easily explained on the basis of a ring- 
closure, as described for bisabolene, eudalene, a CH compound, could only 
have been formed from a Ci 6 compound by loss of an angular CH 3 group. 
The structure of the sesquiterpene belonging to this eudalene group shows 
an architecture which we find quite often in the higher terpenes, resin 
acids and carotenoids, i.e., a cyclogeraniol or cyclocitral structure. These 
ring compounds can readily be prepared from aliphatic terpenes under the 
influence of concentrated acids, such as phosphoric and sulfuric. Deriva- 
tives of this type of cyclization are found among the ionones. The bicyclic 

17 Vesterberg, B*>r. 36 (1903), 4200. 

18 Diels and Karstens, Ber. 60 (1927), 2323. 

1? Zelinsky, Ber. 44 (1911), 3121. /. Russ. Phjs. Chem. Soc. 43 (1911), 1220. 


geranlol Unaloul farnesol 




pymene cadi no no isomer cadaleno 

FIG. 2.14. Cyclization in the Sesquiterpene scries, Cadalcne formation. 



sesquiterpenes of the eudalene type may be described as being of this cyclo- 

geraniol ring-closure structure followed by a ring-closure of the linalool > 

terpinene type (Fig. 2.15). To this group belong the alcohol, eudesmol, 20 
and the lactone, santonine 21 (the active principle of Levant wormseed 
[Flores cinae], well known for its anthelmintic properties). 

jS-cyclocitral ft- eudesmol santonlne 

FIG. 2.15. Cyclization of the Sesquiterpene series, Eudalene formation. 

The third method by which we may derive certain natural sesqui- 
tcrpenes from an aliphatic chain results in compounds which are present in 
some oils and which give a blue color on delo'drogenation. Such bicyclic 
terpene derivatives, guaiol and vetivone for example, when treated with 
sulfur or selenium, are oxidized by removal of hydrogen ; a stable system of 
conjugated and cross-conjugated double bonds in the rings is established 
and intensely blue hydrocarbons are formed. Those so-called azulcncs, 
mixed with yellow components, are responsible for the green color of many 
oils. This color is not caused by the presence of copper compounds from 
the stills as was formerly believed. 

It is worthy of remark here that the blue color which appears on the 
freshly cut surfaces of some mushrooms is due to the formation of the same 
azulene as that obtained from the guaiol in the oil of guaiac wood, and from 

20 Ruzicka, Plattncr and Fiirst, Helv. Chim. Ada 25 (1942), 1364. 
21 Clemo, Haworth and Walton, J. Chem. Soc. (1929), 2368; (1930), 1110, 2579. Ruzicka 
and Eichenberger, Helv. Chim. Acta 13 (1930), 1117. 


many sesquiterpenes in other oils, i.e., guaiazulene. 22 The investigations of 
Ruzicka and of Pfau and Plattner have shown that these azulenes or their 
hydrogenated precursors consist of a five- and a seven-membered ring fused 
together, wherein the methyl and isopropyl side chains are placed in such a 
manner that we may describe the compound as being formed from an ali- 
phatic sesquiterpene such as farnesol. This unrolling and connecting of 
different carbon atoms of a Ci B chain can be done in several ways. At 

FIG. 2.16. Cyclization in the Sesquiterpene series, Azulene formation. 

present, the structures of two of these azulenes (Fig. 2.16) derived from 
vetivone of vetiver oil and guaiol of guaiac wood are definitely estab- 
lished, 23 - 24,26,26,27,28,29 an( j syntheses of many azulenes have made this type 

22 Willstaedt, Ber. 69 (1936), 997. 

23 Naves and Perrottet, Helv. Chim. Acta 24 (1941), 1. 

24 Plattner and Lemay, Helv. Chim. Acta 23 (1940), 897. 

25 Plattner and Magyar, Helv. Chim. Ada 24 (1941), 191. 
28 Plattner and Magyar, Helv. Chim. Acta 25 (1942), 581. 

27 Pfau and Plattner, Helv. Chim. Acta 19 (1936), 865; 22 (1939), 640. 

28 Ruzicka and Rudolph, Helv. Chim. Acta 9 (1926), 118. 

29 Ruzicka and Haagen-Smit, Helv. Chim. Acta 14 (1931), 1104. 


of compound easily available. Through the formation of well-characterized 
molecular addition products with picric acid and trinitrobenzene, the azu- 
lenes, in addition to cadalene and eudalene, have become a welcome tool 
for identification of the carbon skeletons of a number of unknown sesqui- 

If the rule of the regular head-to-tail union of the Cs units fails, and if 
no known dehydrogenation product betrays the general structure, the diffi- 
cult road of gradual degradation has to be followed. Such has be<n the 
case, for many years, with the investigations of the structure of caryo- 
phyllene and cedrene. 

After the general structure has been established, important details 
such as position of double bonds and substituents have to be settled. Ex- 
cellent examples of this type of work can be found in Ruzicka's publications. 
By the use of certain methods (chiefly oxidation) on original, dehydrated, 
or on partially hydrogenated products, we obtain compounds for the most 
part complex and unknown. They may, however, indicate combinations 
of groups such as carbonyl and carboxyl and thus facilitate the choice 
among a number of proposed formulas. This elimination procedure has 
been very fruitful in the sesqui- and higher terpene groups. Its obvious 
limitation makes us welcome new direct methods of attack, such as that 
employed in determining the position of the nuclear double bonds in dextro 
pimaric acid, 30 which consists in marking the position of the double bond by 
oxide formation followed by substitution with a methyl group and dehydro- 
genation to a methyl substituted aromatic compound. 

Campbell and Softer 31 used this method to revise the position of the 
double bonds in the cadinene and isozingiberene formulas of Ruzicka. 
Ruzicka's degradation acids obtained from cadinene agree with the new 
formula as well as with the old one, but the new formula does not agree 
with the oxidation results on the tricyclic sesquiterpene copaene which gives 
the same dihydrochloride as cadinene. In such cases doubt arises about the 
homogeneity of the copaene and the cadinene, since it is possible that 
cadinene hydrochloride obtained from fractionated copaene actually belongs 
to cadinene, the latter being present as an impurity (Fig. 2.17). 

This example emphasizes the great need for care in the purification of 
the substances under investigation. Crystalline derivatives rarely form 
quantitatively, and hence we cannot be sure that we are dealing with a 
homogeneous compound. It is to be expected that the application of 
chromatographic adsorption will contribute a great deal to the clarification 
of these problems. 

80 Ruzicka and Sternbach, Helv. Chim. Ada 23 (1940* 124. 
31 /. Am. Chem. Soc. 64 (1942), 417; 66 (1944), 1520. 


igozinglbcrcnc dl hydro- 

(formerly cadinene dlhydrochlorlde) 

FIG. 2.17. Structure of Cadinene. 

, ; -dimctliy Icadalcne 



The members of the next group of compounds contain 4 isopentane units; 
hence the possibilities of coupling such units are much more numerous than 
they were in the previous groups. These compounds are difficult to study, 
since the separation techniques are limited through the high boiling points, 
the increased chances for isomerizations, and the similarity of their physical 
properties. Fully established structures in the diterpene series are, there- 
fore, few and belong chiefly to some commercially important products 
among them the resin acids from rosin, 32 galipot 33 and kaurikopal, 3 ' and 
compounds like vitamin A and the chlorophyll alcohol phytol (Fig. 2.18). 


at -cam phorc no 

!H 2 OH 

abieUc acid 
FIG. 2.18. Ditorponos. 

D-pimaric acid 

With the exception of a-camphorene, 35 sclareol, 36 and related manoyl 
oxide and manool, the structures of the diterpenes which occur in the highest 
boiling fractions of the essential oils are not yet satisfactorily established. 
This group is at present going through the same early stages of develop- 

Ruzicka, Sternbach and Jegcr, Helv. Chim. Ada 24 (1941), 504. 

88 Ruzicka and Sternbach, ibid. 23 (1940), 124. 

84 Ruzicka, Bernold and Tallichet, Helv. Chim. Ada 24 (1941), 223. 

35 Ruzicka and Stoll, Helv. Chim. Ada 7 (1924), 271. 

36 Ruzicka, Seidel and Engcl, Helv. Chim. Ada 25 (1942), 621. 



ment, i.e., a sharper characterization, as the monoterpenes fifty years ago. 

A crystalline diterpene phyllocladene has been found, which appears to be 

identical with sciadopitene and 
dacrene isolated from other 
sources and isomeric with podo- 
carpene and isophyllocladene. 37 
Dihydrophyllocladene is found to 
be identical with the lignites 
(fossil resins) : hartite, bombiccite 
and hofmannite. 38 ' 39 To find still 
higher isoprene homologues, the 
separation technique with steam 
distillation is unsatisfactory and 
we have to resort to reduced pres- 
sure distillation or solvent ex- 
traction techniques. Through the 
use of these methods, products 
have been isolated which show a 
continuation of the branched C 5 
building plan and consist of six 
C 5 units. Some of these we find 
in the nonvolatile part of the 
resins like /3-amyrin; other ex- 
amples are boswellic acid fro r u in- 
cense and betulin, the white pig- 
ment of the bark of birch. In- 
teresting members are found in 
woolfat as lanostcrol, 40 in quinine 
bark as chinovic acid, 41 in cloves 
and olive leaves as oleanolic acid 
(Fig. 2.19). This acid is also 
known to be present as glycoside 
in several plants. These types of 
glycosides, as a result of their dc- 

oleanollc acid 1 

FIG. 2.19. Triterpcnes. 

1 Bilham, Kon and Ross, J. Chem. 
(1942), 532. Cf. Ruzicka, ct al., Helv. Chim. 

Ada 26 (1943) 227, 280. Noller, Ann. Review tergent reactioll; have received the 

Biochem., 14 (1945), 381. 

name of saponins. Many drug 

plants, such as sarsaparilla and smilax, owe their pharmacological action to 
the presence of these C 3 o compounds. 

37 Briggs, "Review of the Diterpenes," Rep. Meeting Australian New Zealand Assocn. 
Adv. Sc. 23 (1937), 45. 

88 Soltys, Mvnatsh. 53-54 (1929), 175. 

Briggs, J. Soc. Chem. Ind. 60 (1941), 226T. 

40 Bellamy and Doree, /. Chem. Soc. (1941), 172. 

tt Ruzicka and Prolog, Helv. Chim. Ada 20 (1937), 1570. 



lycopene C 40 H M 

The structure determination of these tetracyclic triterpenes relies heavily 
on the formation of picene derivatives through dehydrogenation. Since all 
angular methyl groups are removed 
in this process, special degradation 
reactions should provide proof of 
their position. This difficult struc- 
tural detail has not yet been ac- 
complished for all methyl groups, 
and their present fluctuating posi- 
tion in the proposed formulas rests 
largely on the application of the 
"isoprene hypothesis." 

The simple symmetrical consti- 
tution of the triterpene squalene 
(Fig. 2.19) present in liver of sharks 
and many vegetable oils 42 permit- 
ted rapid progress in the elucidation 
of its structure, and even its syn- 
thesis has been accomplished by 
combining 2 mols of the acyclic 
sesquiterpene alcohol farnesol. 43 - 44 

This symmetrical build up, 
which we see for the first time in 
squalene, is quite common in the 
next group, viz., the tet rater penes. 
The known members of this group 
belong to the yellow and red crys- 
talline carotenoid pigments from 
plants and animals. The carbon 
skeleton of these compounds can 
be described as a doubling of a 
regularly built diterpene. In lyco- 
pene (Fig. 2.20), the red pigment 
of the tomato, we find a chain of 
32 carbon atoms with 8 methyl 
side chains. In most carotenoids 
the ends of the long chain have 
formed a cyclogeraniol type of cyclization, as in 0-carotene and xanthophyll 
(Fig. 2.20). 

44 Taufel and Heiman, Biochem. Z. 306 (1940), 123. 

48 Schmitt, Liebigs Ann. 547 (1941), 115. 

44 Karrer and Helfenstcin, Helv. Chim. Ada 14 (1931), 78. 

-carotene C 40 H W 

FIG. 2.20. Tetraterpenes. 


The presence of a large number of conjugated double bonds (14 in lyco- 
pene) distinguishes this group from other terpenoids, and is responsible for 
the red and yellow colors which are so characteristic of this group of sub- 

As a result of our lack of knowledge of representatives belonging to the 
intermediate groups, we must look for the next higher terpenes in a number 




dfc, c- 


UH V" a 


.[ 1 

1 I 

CH 2 

CH 2 CH, 

/ w 

'? / \ 

y / 

f ' T 
A A 


*s / 

i^T-i OTT 
on 2 yn 2 


3 CH 2 


H,C CH, 


CH 2 CH, 

FIG. 2.21. Mixed building schemes. 
1 H. Wieland and E. Martz, Ber. 59B (1926), 2352. 

of compounds which have attracted the attention of investigators on ac- 
count of their elastic properties. The different rubbers from Hevea, Guay- 
ule, etc., belong to this polyterpene group and contain up to several thousand 
CB units. 

While all of these compounds can be divided completely into branched 
Cs chains, a number of natural products contain structures in which we can 



recognize one or more of these units, but which we cannot fully describe in 
this way. In such cases some of the carbon atoms are left over; these form 
often a straight chain, as in cholic acid and cholesterol. Also in humulone 
(Fig. 2.21) the connection with the terpene compounds is unmistakable; 
nevertheless, we cannot fully divide the molecule into branched 5 chains. 
In some cases the recognition of such building principles },er/es as a 
guide in the laboratory synthesis, and also indicates a possible biogenesis. 
An interesting illustration is furnished by the structure of cannabic iiol, one 
of the constituents of Egyptian hashish. We can easily recognize in this 
molecule the structures of cymene or l-mcthyl-4-isopropcnylbenzene, the 
first of which form the main part of the essential oil of hashish 45 (Fig. 2.22). 


l-methyl-4-i8oproi>enyl- j'-cymene oliretol cannabid 


FIG. 2.22. Constituents of Oil of Hashish. 

1 Adams, Loewe, Pease, Cain, Wearn, Baker and Wolff, J. Am. Chcm. Soc. 62 (1040), 

Similar considerations led to the synthesis of the antisterility vitamin E 
which is formed by coupling phytylbromide with trimethylhydroquinone, 
whereas the antihemorrhagic vitamin Ki is synthesized by condensing the 
same bromide with the sodium salt of 2-methyl-l,4-naphthoquinone. 46 

The second major group of oil components contains only straight chain 
hydrocarbons and their oxygen derivatives: alcohols, aldehydes, ketones, 
acids, ethers and esters. These essential oil hydrocarbons range from n-hep- 
tane, which forms 90 per cent of the oil of Finns sabiniana and P. jcffreyi, to 
compounds with 15-35 carbon atoms. 47 The higher paraffin-like materials 
may crystallize out during cooling and storage of the oils and are called 
"stearoptenes." The number of carbon atoms in some of these hydrocar- 
bons suggests a connection with the natural occurring fatty acids through de- 

45 Simonsen and Todd, /. Chem. Soc. (1942), 188. 

46 Dam. Ann. Review IX(1940), 362. 

47 Schorger, Trans. Wisconsin Acad. Sci. 19 (1919), 739, 752. 


carboxylation or ketone formation. The formation from the wax alcohols 
through dehydration and reduction is also held possible. 48 

The alcohols, aldehydes and ketones are quite often contained in the low 
boiling fraction of the volatile oil. A typical example is found in the so- 
called leaf alcohol (cis- or rans-hexen-3-ol-l), carrier of the odor of grasses, 
green leaves, etc. Oxidation of the alcohol with chromic acid furnishes a 
hexenal which has been recognized in many green plants, including tea, ivy, 
clover, oak, beech, wheat, robinia, black radish, violet leaves and cucumbers. 
However, the volatile oil of cucumber consists largely of nonadiene-2,6-ol-l 
with some nonadiene-2,6-al-l 49 (Fig. 2.23). This aldehyde has also been 
recognized in the leaf oil of violets. 50 

CH 8 CII 2 CH=CH CII 2 CH 2 -OH 
leaf alcohol 





FIG. 2.23. 

In this group are also included the many fatty acids which occur free 
or esterified with alcohols of different chain length and different degrees of 
saturation. This group is present in a number of volatile oils from fruit. 

The third major group of essential oil components comprises a number of 
important flavor and perfume constituents derived from benzene and more 
specifically from n-propyl benzene. As in the preceding groups, we find 
these compounds in many stages of oxidation. The aromatic ring may carry 
hydroxy, methoxy and methylene dioxy groups; the propyl side chain may 
contain hydroxyl or carboxyl groups, or form a part of a lactonc group, as in 
coumarin and its many derivatives 51 (Fig. 2.24). Many members of this 
group are related through simple chemical reactions. For example, on 
isomerization followed by oxidation, eugenol is converted to the corre- 
sponding vanillin (Fig. 2.25), the flavoring principle of the vanilla bean. 

"Butt. Univ. Wise., Serial No. 1919, Gen. Series No. 1703 (1934). "Phytochemistry," 
III, Kremers and collaborators. The methane series of hydrocarbons. 
"Takei and Ono, J. Agr. Chem. Soc. Japan 15 (1939), 193. 
60 Ruzicka and Schinz, Helv. Chim. Ada 25 (1942), 760. 
" Sethna and Shah, Chem. Rev. 36 (1945), 40. 


/ CH \/\' A A* 


c CH in, i L L, 

o Y o 7 V 

H 2 C H 2 C O 

eafrole myristicin 

(sassafras oil) (nutmeg ,u) 

FIG. 2.24. Aromatic oil constituents. 

1 Haworth and Kelly, J. Chem. Soc. (1937), 384. 

2 Ishiguro, J. Pharm. Soc. Japan 56 (1936), (Abstracts in German), 08. 

A X CH 2 C 

oc AK, ,,,,/ 

I II II oxidation ^ I 

6 CH CH, /\/ H 

H/ V H/ V 


eugenol vanillin 

FIG. 2.25. Relations between aromatic oil constituents. 

This group of compounds shows a definite relationship to some of the resins 
with aromatic structures, like matairesinol, 52 which represent a doubling 

Haworth and Slinger, /. Chem. Soc. (1940), 1098. 


of the propyl benzene structure. This dimerization has been demonstrated 
in vitro for isoeugenol methyl ether which is doubled into fo'sisoeugenol 
methyl ether 53 (Fig. 2.26). It is probable that a condensation of a large 


\ H 


CH CH 2 


H.CO C C c-CH, 

\H CH 



4 L 





Isoeuflrenol methyl ether 

/ V VcBW 




Wa-lsoouffcnol methyl ether 

>-C C i^CH 2 OH 




laolarlclresinol cubobln 

FIG. 2.26. Relation between aromatic oil constituents and rcsinols. 

number of analogous units has led to the formation of lignin, the widely 
distributed component of woody tissues. Such a relation is comparable to 
the formation of rubber from the smaller terpene building units. A some- 
what more distant connection can be seen in the f on^ation of the anthocyans 

M Muller and Hartai, Ber. 75B (1942), 891. 


and flavones, since propyl benzene derivatives have been postulated as 
taking part in the biosynthesis of these plant pigments. 

From this short account of our chemical knowledge of the essential oil 
components and their near relatives, it is clear that their study must have 
occupied the minds of a large number of chemists interested in natural 
products. In numerous cases the purification, characterization, structural 
determination and synthesis of a single terpene has been the lifetimf work 
of many of the terpene chemists. ' 

The difficulties are immediately apparent when the starting material 
arrives in the laboratory. Separation has to be accomplished on a large 
diversity of compounds, since the only links between them are their plant 
origin and their volatility. In addition, many of the constituents are easily 
converted into other compounds with similar properties. The investigation 
of the essential oils has, therefore, served as a hard schooling in chemical 
separation techniques, in which none of the existing methods, physical or 
chemical, can be neglected. When the oils are obtained from the plant by 
steam distillation, the steam carries over the volatile component at a tem- 
perature of somewhat less than 100.* This, however, does not represent the 
actual boiling point of the oil components. At the boiling point of a mixture 
of oil and water, the sum of the partial pressures of oil and water is equal to 
the atmospheric pressure. The boiling temperature of the steam and vapor 
mixture is, therefore, lower than the boiling temperature of water alone. 

In a mixture of oil of turpentine and water, which boils at 95.6 at 760 
mm. pressure, the vapor pressure of the oil contributes 113 mm., the water 
647 mm. Without the help of the water vapor, the bulk of most oils would 
distill at 150-300, at which temperature labile substances would be de- 
stroyed and a strong resinincation would occur. With the aid of steam dis- 
tillation, the majority of these compounds are carried over a few degrees 
below the boiling point of water. Vapor pressure data 64 - w - 56 67 of single 
components make it possible to calculate their boiling points by steam dis- 
tillation and the proportion of oil and water which is distilled at different 


While steam distillation is a simple procedure, we cannot per se assume 
that a steam distilled oil is identical with the oils as occurring in the plants. 
Several cases are known where certain compounds are formed by the action 
of the steam. These are for the most part degradation products of carbo- 
hydrates, like furfural. Loss of water from alcohols and hydrolysis of esters 

* NOTE. All temperatures in this book are given in degrees centigrade unless otherwise 

M Charabot and Rocherolk*. Compt. rend. 135 (1902), 175. 

66 Pickott and Peterson, Ind. Eng. Chem. 21 (1929), 325. 
M Under, J. Phys. Chem. 35 (1031), 531. 

67 Schoorl, Rec. trav. chim. 62 (1943), 341, 350, 354, 358, 363, 366, 375. 


will result in the formation of new hydrocarbons and acids. Likewise, nitro- 
gen compounds often have a secondary origin. This destruction usually 
runs parallel with the loss of the delicate nuances in smell and is a certain 
indication that changes in the original composition of the oil have taken 
place, a matter of concern for both production and research departments. 

Since the oils contain chemical compounds of many classes, it is often 
desirable to remove at least those groups of substances that contain more 
reactive groupings than the hydrocarbons, among them acids, bases, phen- 
ols, ketones and aldehydes. The oils are, therefore, treated with dilute 
aqueous alkali solutions to remove the acidic substances, or with bases to re- 
move the acids, with sulfite, bisulfite or Girard's reagent to isolate ketones and 
aldehydes, and sometimes with phthalic anhydride to remove the alcohols. 

In the oil layer or in the solvent extract of the steam distillate (including 
that of the distillation water), compounds boiling lower and higher than 
water are found, and the desirability of fractionating the original, or the 
treated oil, into fractions which preferably contain only one component Is 
indicated. When we assemble the fractionation data in a graph and plot 
the quantity of oil distilled within a certain temperature interval along the 
ordinate, although the abscissa shows the boiling points, we notice in the 
fractionation curve of different oils maxima indicating the presence of dis- 
tinct components of the oils. In the fractionation of the American oil of 
peppermint (Illustration 2.1), a typical terpene oil, the first volatile com- 
ponents which distill are small quantities of two compounds which were 
postulated by some investigators as the building stones of the branched C s 
chains, viz., acetone and acetaldehyde, accompanied by dimethyl sulfide, 
a compound containing sulfur. These are followed by the hemiterpenes, 
isovaleraldehyde and isoamyl alcohol; and these in turn are followed, at a 
temperature of approximately 150, by a number of compounds, which by 
.analysis are shown to consist of carbon and hydrogen only. Several 
small maxima in the boiling point curve indicate the presence of several 
of these terpenes. At this stage the determination of physical constants, 
such as specific gravity, refractive index and optical rotation, may aid 
considerably in indicating the nature of the terpenes. 

With the exception of camphene and bornylene, all the terpene hydro- 
carbons are liquid at ordinary temperatures, and their tendency to crystal- 
lize at lower temperatures is negligible. The tendency to form a distinct 
crystalline pattern can be greatly increased when polar groups are intro- 
duced into the molecule. The first crystalline derivative of a hydrocarbon 
to be prepared in this way is the so-called "artificial camphor" obtained by 
Kindt 58 in 1803, when he passed hydrogen chloride into oil of turpentine. 

58 Butt. Univ. Wise., Serial No. 1813, Gen. Series No. 1597 (1932). "Phytochemistry," 
II, Kremers and collaborators. Chemical properties of hydrocarbons. 



The systematic study of these methods is, however, due to Wallach, 69 who 
about fifty years ago introduced several more of these procedures. Since 
the double bonds are the only reactive points in the terpenes, these groups 
are introduced into the molecule by simple addition reactions to the double 
bond. In this way, halides, dihalides, nitrosohalides, nitrosites and nitro- 
sates are formed. Through these reactions, the hydrocarbon derivatives 
may crystallize even from impure fractions, and their identification is 

Frac donation 

Oil of Peppermint 


100 200 300 

Boiling temperature in C at 760 mm 

ILL. 2.1. 

possible through comparisons of the melting points of the same derivatives 
of known terpenes. Modern chemistry has added only a few more reagents 
to this list, among them, maleic anhydride for the characterization of com- 
pounds with conjugated double bonds 60 - 6l - 62 (Fig. 2.27). 

When the distillation is continued, the next large group of fractions 
boils at about 200-230. They consist mainly of the oxygen derivatives of 
the terpenes, CioIIisO, and in our fractionation example of peppermint oil, 
a fraction of menthonc is obtained, followed by a larger fraction of menthol. 
While some oxygen derivatives in peppermint oil are crystalline, in 
many other oils these have to be characterized by reaction products with 
certain identifying reagents, such as phenylisocyanate and nitrobenzoyl- 
chlorides for alcohols, and nitrophenylhydrazines for ketones and aldehydes. 

Ruzicka, "The Life and Work of Otto Wallach," /. Chem. Soc. (1932), 1582. 

M Diels and Alder, Liebigs Ann. 460 (1928), 98. 

Birch, /. Proc. Roy. Soc. N. S. Wales 71 (1937), 54. 

Goodway and West, J. Soc. Chem. Ind. 56 (1937), 472T. 


The next group of compounds we encounter in the fractionation is again 
of a hydrocarbon nature. We have come into the region of sesquiterpenes 
Ci6, and these Cis compounds are again followed by their oxygen derivatives 
which in turn are followed by diterpenes. If the oils contain a number of 
benzene and aliphatic compounds their fractions will be superimposed on 
this general scheme. 

The boiling point regularities observed in the fractionation of the oils 
are clearly expressed in a graph showing the boiling points of the normal 


limoneue dlb>droclioiide a-plnene nitrosochorlde 

a-pbellandrene Unalelc anhydride addition product 

FIG. 2.27. Crystalline reaction products of Monotorpencs. 

hydrocarbons of different chain length (Illustration 2.2). If the ordinate is 
plotted on a logarithmic scale nearly straight lines are obtained. 63 The boil- 
ing temperatures of the essential oil hydrocarbons are usually lower than 
those of the straight chain compounds, since branching of the chain tends to 
lower the boiling point. This counterbalances the possible rise in boiling 
point through the introduction of unsaturation. The net result is a boiling 

M Butt. Univ. Wise., Serial No. 1019, Gen. Series No. 1703 (1934). "Phytochemistry," 
III. The methane series of hydrocarbons (Foote, Relationship between chemical constitu- 
tion and boiling points of hydrocarbons of the methane series). 



interval, for tha majority of monoterpencs, of from 155 to 185 (represent- 
ing the range of boiling points from pinene to terpinolene), whereas the 
straight chain normal decane boils at 175. 

A further look at the graph shows some irregularities at 300, which indi- 
cate that even the normal saturated hydrocarbons are destroyed. To avoid 
this disagreeable behavior, a reduction in pressure, resulting in a lowering of 
the boiling point, is resorted to when we intend to continue the fractioiiation 
beyond this point. In the case of the much more sensitive terpenok, this 
phenomenon Avill appear much earlier, and it is usually not safe to raise the 









20 30 40 50 

Number of Carbon Atoms 



ILL. 2.2. Boiling points of straight-chain hydrocarbons. 

outside bath temperature to higher than about 180. Thus a fraction 
containing sesquiterpenes (Ci 5 ) boiling at 250 at ordinary pressure can be 
investigated by distilling at aspirator vacuum of 15 mm. at about 120, 
or at a still lower pressure of 0.1 mm. at about 60. 

In this way and by applying ultra high-vacuum, it is possible to study 
sfcill higher terpcnc homologues. But gradually these compounds become 
too complicated and too fragile to give satisfactory fractionation data. 
For this reason, it is desirable to obtain these compounds, not by steam 
distillation, but by extraction with solvents, such as alcohol, acetone or 
petroleum ether, or by chromatographic adsorption analysis. Following 
these procedures we will also find the compounds of the isoprene structure 
which have taken part in reactions which made them nonvolatile, such as 
the combination of the diterpene alcohol, phytol, with the complex phorbine 
ring system of chlorophyll. 


When the purified fractions are characterized by preparation of crystal- 
line derivatives, and when these are compared by melting point and mixed 
melting point with the known derivatives, there remain always some frac- 
tions which cannot be characterized in this way. In, such cases, chemical 
degradations of the molecules have to be applied. The principle involved 
in these degradations consists of breaking up the molecule into smaller 
parts until the pieces have become so simple that they can be recognized. 
For this purpose, oxidation with ozone, potassium permanganate and chro- 
mium trioxide is often used. Sometimes several of these degradations may 
be necessary before the pieces obtained are small enough to be identified. 
On the basis of these degradations, a possible structure is postulated and 
attempts are made to confirm this structure by synthesis. This work has 
been carried out on about 500 constituents of essential oils. One-fifth of 
this number is made up of monoterpenes, and only a start has been made on 
the investigations of sesqui- and higher terpenes. In view of the greatly 
increased possibility of structural isomerism, every time 5 carbons are 
added to a molecule we may look forward to the addition to our present 
knowledge of a great number of the higher terpene homologues when a more 
extensive survey is made. 


In the foregoing discussion of the components of the volatile oils, we saw 
that they consist of a variety of compounds which belong to all chemical 
classes. We cannot expect to find a common history for such varied rub- 
stances. We do observe, however, certain chemical relations between a 
number of the components. Indeed, it was this similarity that led us to 
discuss the results of chemical research in terms of four groups, i.e., straight 
chain hydrocarbons, benzene derivatives, terpenes and miscellaneoos com- 
pounds. In view of their structural similarity straight chain hydrocarbons 
are generally considered as connected with fatty acid metabolism, while 
benzene and propyl benzene derivatives are connected with carbohydrate 
metabolism. The group which gives rise to most of the speculation, how- 
ever, comprises the terpenes. 

We have seen that members of this series could conveniently be described 
as divisible into branched C 6 chains. This statement refers to an established 
fact; but we enter the field of speculation and hypothesis in assuming that 
such a structure as a C B chain actually represents the basic unit in the forma- 
tion of the terpenes in the plants. . 

Many terpene investigators have risked guesses as to the nature of this 
basic unit, but few have tried to support their hypothesis by experiments. 
One of the oft-mentioned precursors (as we may call them) is isoprene 
(C 6 H 8 ), belonging to the group of hemiterpenes. This compound in its 


turn is postulated to arise from the condensation of acetone or derivatives 
like dihydroxyacetone and acetaldehyde. 64 Through polymerization and 
addition of isoprene to higher terpenes, terpene homologues can be pre- 
pared. 66 Among several condensation products dipentene and a bisabolene- 
like sesquiterpene can be identified 66 (Fig. 2.28). When such reactions are 

2 isopronc molecules > dipentene 

CH 3 CH S CH 3 

A/"' A A A A 1 ' 

H 2 C PIC Cll, ht . at ^ H 2 C CH CH 2 H 2 C C CH 2 

H 2 C V ,C CH 3 H 2 C V CH 2 JO CH, H 2 C CH 2 ,C~ CH, 

V ^ \,,V \nV 

H,C CH, II 3 C CH, 

isopiene -j- UiDcntene : > blsabolene 

FIG. 2.28. Polymerization of Isoprene. 

carried out under simultaneous hydrogenation or hydration, the reactive 
ends of the molecules are saturated and further condensation and resinifica- 
tion are thereby largely prevented. Following this principle, Midgley et al. 67 
carried out the condensation of isoprene under reducing conditions with 
sodium amalgam and obtained the terpene hydrocarbon 2,6-dimethyloctane. 
Wagner-Jauregg 68 condensed two mols of isoprene in the presence of sul- 
furic and acetic acids. Under these conditions water is added to the double 
bonds and goraniol can be isolated from the condensation mixture (Fig. 2.29). 
Ingenious as these experiments are, they do not furnish proof of the isoprene 

The same can be said for the hypothetical precursor 3-methylbutenal 
(Fig. 2.30). This compound would very well satisfy the demands for a 
reactive precursor. In vitro experiments with 3-methylbutenal, with its 
conjugated carbonyl group and double bond, clearly demonstrate great 
reactivity and readiness to react with many other molecules. Fischer 69 

64 Aschan, "Naph ten verb indungen, Terpene und Campherarten," Walter De Gruyter & 
Co., Berlin and Leipzig (1029), 127. 

66 Forisrhriite Chem. Org. Naturstoffe 3 (1939), 1. Bedeutung der Diensynthese fur 
Bildung, Aufbau und PMorsehung von Naturstoffen, Diels. 

M Egloff, "Reactions of Pure Hydrocarbons," Reinhold Publishing Co. (1937), 759. 

67 J. Am. Chem. Soc. 51 (1929), 1215; 53 (1931), 203; 54 (1932), 381. 

68 Licbigs Ann. 496 (1932), 52. 

69 Fischer and Ix5wcnberg, Liebiga Ann. 494 (1932), 263. 




CH a 

HaC CH 3 

2 iHOpreno 



^HaC 9H 4H 












,C CH, 




H 2 

C CH, 

II 3 C 

2,6-dimctli) 1 octane 

FIG. 2.29. Dinierization of Isoprcnc. 

H 3 C CH 

H,C CH 3 


Fia. 2.30. Terpene synthesis from 3-Methylbutenal. 




^ / .s 

\ / 2 



^ 2 




i 1 

=CH C 





^ 1 

O j 


/ N 


W K ^ 











1 1 




+l l 



















/ \ 



i i 

> w O 




hH S 










+ '+1 






O -3 








K c 

V | 
J. s 




9 1 


,/ G x ' S 




O W 



w w 


succeeded in this way in building up dehydrocitral which might easily serve 
as the basic substance for aliphatic, as well as cyclic, terpenes. 

An added proof would be the synthesis of 3-methylbutenal from acetalde- 
hyde and acetone. Unfortunately, this follows a different addition scheme 
in vitro; and others have, therefore, suggested the formation of 3-methyl- 
butenal by condensation of acetone with pyruvic acid, followed by de- 
carboxylation. This would also furnish an explanation of the presence of 





H,C CH, 



il^Y v-d* 

H xJ t 

\ V H 

IK/ \ II 

no\ /\ 



r l 



I/ U1J 

' I/ OH 

H,C CH, 

H 3 C CH, 


H,C CH, 






H,C CH, 

M ^ CH 


\ X H 





x^ A 11 rn 


> All lei penes 

/ \ 

/ \ 

H,C CH, 

H,C CH, 







acetoacettc aciU-f acetone 



orcinol -f acetone 

FIG. 2.32. Hypothetical Terpene synthesis from Acetone, Acetaldehyde 
and Acetoacetic acid. 


isovaleric acid and pyroterebic acid in the oil of Calotropis procera, where the 
latter acid occurs esterified with a diterpene alcohol 70 (Fig. 2.31). 

However, Francesconi 71 can claim these compounds for his scheme in 
which isoamyl alcohol has a prominent place. This alcohol is obtained 
through degradation of carbohydrates, proteins or amino acids like leucine. 
From leucine, pyroterebic acid and isovaleric acid can be derived with great 
ease. Huzita 72 follows Ostengo in considering isovaleraldehyde to oake a 
prominent place among the number of proposed precursors. Still another 
possibility is mentioned by Simpson, 73 who couplet acetoacetic acid with 
2 mols of acetone to obtain the monocyclic terpenes. The aliphatic terpenes 
are constructed on paper by linking 3 mols of acetone with one of formalde- 
hyde (Fig. 2.32). Similar hypothetical schemes, using 2 acetone and 2 
acetaldchyde molecules, are published by Singleton, 74 and Smedley-Mac- 
Lean. 76 Available experimental data on these reactions speak against these 
types of condensation and special factors and conditions have to be postu- 
lated in order to account for the directive nature of the plant processes 
(Fig. 2.32). 

Since none of these theories can be definitely rejected or accepted, it is 
clear that the presence of the branched chain represents a weak foundation 
on which to build hypotheses on the formation of the terpenes. We also 

CH S CH 3 CH, 

I / I / I / 

H,C C=/C-CH 2 -CII 2 -C=/C-CH 2 -CH 2 -C^t--CH 2 'OH 

/ 1 , / 1-, / L_ 


/ / / / / / 

CH, CH, CH, 

* I I I 

H,C-C = CH-CH 2 -CH 2 -C=CH-CH 2 -CH 2 -C=CH-CH 2 -OH 

fnrnosol tormatloD 

FIG. 2.33. Terpene synthesis according to Emde. 

have to admit the possibility that the 5 carbon units into which we can 
divide the molecules of the terpenes may have their origin in larger units. 
This suggestion was made by Emde, 76 who postulated a physiological syn- 
thesis from sugars, through a coupling of levulinic acid-like molecules, 
followed by loss of CO 2 and the addition of smaller fragments of sugar meta- 

70 Hesse, in "Organic Chemistry" by Fieser and Fieser (1944), 981. 

71 liwistn ital. esscnze profumi 10 (1928), 33. 
78 J. Chcm. Soc. Japan 60 (1930), 1025. 

73 Perfumery Essential Oil Record 14 (1923), 113. 

74 Chemistry Industry (1931), 989. 
76 J. Chern. Soc. 99 (1911), 1627. 

76 Hclv. Chim. Acta 14 (1921), 881. 




**H / 





*5/p3 <1 a 3 

I i 

2 o3 


8 *-* 
ly-8 .!.'& 


o o v 



B ffi 

O x ^ 

W W/ -3 

o-o p 

x \ L 

^ ^ 





9 ,5- 

1 K/ 




















s , 






holism when necessary (Fig. 2.33). The chief value of this clever hypothesis 
is probably that it points to other ways of constructing branched .molecules. 
This applies especially to the theory of Hall, 77 who attributes the formation 
of terpenes and benzene derivatives to the condensation and degradation of 
sugar derivatives. In this way different hypothetical "half molecules" 
were postulated which are finally combined to give the desired structures. 
An example of the proposed formations of a terpene precursor is pictured in 
Fig. 2.34. 

Extensive schemes for the derivation of other terpenes and the further 
synthesis of higher terpenes can hardly contribute to the acceptance of any 
one of these theories, because once a terpene-likc compound is synthesized 
on paper it is not difficult to explain the many combinations of terpenes we 
encounter in nature. Oxydases, reductases, esterases and even special ring- 
closing enzymes ("Kyklokleiasen" of Tschirch) are therefore welcome in- 
struments in the hands of theorists. In vitro many of the terpenes have 
been converted one into the other by simple chemical reactions, which take 
place under physiologically possible conditions. Under the influence of 
light, air and water, we can expect reactions to take place which we observe 
in vitro in improperly stored essential oils, i.e., oxidation and polymerization. 
Free acids, if present, may cause loss of water, cyclization and esterification. 

Considering the long storage of these oils in the plant, it is not astonish- 
ing that analyses of the oils indicate a gradual change in the expected direc- 
tion with the maturing of the plant. Experiments on peppermint show an 
increase in the menthone content with an accompanying decrease in men- 
thol content due to oxidative processes. At the same time, the percentage 
of compounds other than menthol and menthone increases, indicating a 
splitting off of water and polymerization. 

It is very probable that, in a number of cases, especially in oxidation and 
reduction reactions, enzymes play, an important role. Ncuborg succeeded 
in the reduction of citronellal 78 to d-citronellol, and of citral 79 to geraniol 
with yeast. These experiments, extended by Fischer, 80 disclosed certain 
laws which govern the enzymatic hydrogenation of double bonds between 
carbon and carbon, and carbon and oxygen. The double bond conjugated 
with the aldehyde group in citral is slower in its hydrogen uptake than the 
carbonyl group; and we see, therefore, that the formation of geraniol takes 
precedence over the formation of citronellal. When geraniol is subjected to 
further hydrogenation, citronellol is formed, leaving the double bond at Cc 
untouched. Citronellol produced in this way from optically inactive 

77 "Relationships in Phytochemistry," Chem. Rev. 20 (1937), 305. 

78 Mayer and Neuberg, Biochem. Z. 71 (1915), 174. 
79 Neuberg and Kerb, Biochem. Z. 92 (1918), 111. 
* Q Fortachrttte Chem. Org. Naturstoffe 3 (1939), 30. 



geraniol is optically active-dextrorotatory (specific rotation [z>] =4-6) 
as in citronella oil. No further hydrogenation of the isolated double bond 
can be effected in this way, and it is interesting to note that in plants also, 
the hydrogenation has come to a halt at the citronellol stage (Fig. 2.35). 



FIG. 2.35. Enzymatic reductions. 

Substituents greatly influence the speed of the enzymatic hydrogena- 
tions, as seen in the slower hydrogen addition to keto groups, and to double 
bonds on tertiary carbon atoms. Carvone, main constituent of caraway 
oil, when subjected to enzymatic treatment, is reduced with difficulty to 
dihydrocarvone, another constituent of this oil (Fig. 2.36). The absence 
of the totally hydrogenatcd carvomenthol suggests that similar laws are 
followed in the production of these terpencs in the plant. 

These biological reductions can also be followed by studying the excre- 
tion products in urine during feeding or injection experiments. While in 
general, advanced oxidative degradations outweigh hydrogenation processes, 
a careful analysis of the excretion product shows similar reactions, as in the 
more simple experiments with yeast or enzyme-systems. Perhaps due to 


the branching of the chains, the reaction products of terpenes, such as 
citral, geraniol and geranic acid, 81 can be recognized in the urine of rabbits 
after feeding or injection experiments. Fig. 2.37 shows that, notwithstand- 
ing the simultaneous oxidation in other parts of the molecule, the double 

bond in a,/3-position to alcohol, aldehyde 
or acid groups is hydrogenated. Similar 
experiments on citronelloi 82 confirm these 
observations; no reduction of the double 
bond in the isopropylidene group can be 
observed, but further oxidation produces 
dihydro Hildebrandt acid and hydroxy- 
dihydrogeranic acid (Fig. 2.37). 

In jS-ionone, 83 however, where the 
double bonds are conjugated, reduction 
of the carbonyl group and its neighboring 

F.o.2.36. Enzymatic reductions. double bond takcs P hlCC ' leilvin K thc 

double bond between the two tertiary C 

atoms unchanged. Further oxidation introduces a hydroxyl group at one 
of the methyl groups (Fig. 2.38). The agents responsible for similar oxida- 


H 2 OH 





Hildebrandt acid 



dihydro Hiklobrandt 

FIG. 2.37. Oxidation and reductions of Gcraniol in animals. 

tions in the plant are suspected to be of enzymatic nature, but this has 
not been established experimentally. 

Based on the not too improbable assumption that the terpenes present 
in a specific oil are interrelated, several building schemes were developed 
involving a stepwise conversion of the components, starting with a common 

81 Hildebrandt, Z. Physiol Chem. 36 (1902), 441. 

82 Ibid. 

83 Fischer, Fortschritte Chem. Org. Naturstoffe 3 (1030), 30. 



precursor. In this way, Francesconi 84 explained the simultaneous presence 
of citral, citronellal, linalool, dipentene, methyl heptenone and acetaidehyde 
in lemongrass oil. Likewise, Kremers 85 correlated the components of 
American peppermint oil, acetone, acetaldehyde, citral, citronellal, iso- 
pulegol, menthol and menthone. 


hydroxj -dlhj ilto-^3 -lonone 

CH 2 OH 


Fir.. 2.38. Biological oxidations and reductions of /Monone. 

The following biogenesis of the two groups of substances found in the 
oils of American black mint and spearmint was suggested by Kremers. 86 
The names of substances actually found in the oils are italicized, while the two 
reducible groups in the citral molecule are underlined (Fig. 2.39). 

Structural relationship and frequent occurrence in mint and eucalyptus 
oils has been noticed by Read 87 for the terpenes, piperitone, piperitol, 
a-phollandrcnc and A 4 -carene. Piperitone is always accompanied by geranyl 
acetate, from which many cyclic terpenes can be formed. Read, therefore, 
has expressed the opinion that the geraniol is a possible intermediate 
precursor of a number of terpenes. In Eucalyptus macarthuri the chain of 
reaction apparently stopped at the formation of geraniol, since the oil con- 
tains 77 per cent geranylacetate, while in most other species (under different 
conditions in the plant), more advanced transformations take place. 

84 Rivista ital. essenze profumi 10 (1928), 33. 
86 J. Bid. Chem. 50 (1922), 31. 

86 Ibid. 

87 J. Soc. Chem. Ind. 48 (1929), 786. 

HaC O 

C==0 +H.CC 
H,C/ \ 

Acetone + Acetaldehyde 

-H 2 

H 3 C 

H 8 C 

/ + 1L 

\ ' 

2mols -1 mol II 2 O 

H 8 C 



1I,C 11 






H 3 C CH, O 


Citral, CioIIieO 



Citronellal, Ci Hi 8 O 


Menthol, Menthone, Limonene, etc. 

Geraniol, CmllmO 




Terpineol, Cineole, I)ihi/<iro- 
carveol, Carvone, etc. 
in S{>earmint Oil 

in Peppermint Oil 

FIG. 2.39. Biogenesis of Terpenes in Oil of Peppermint and of Spearmint. 

Similar relations are discussed in the genus Orthodon (fain. Labiatae). 
These oils mostly contain major quantities of thymol, carvacrol, cymene, 
cineole, thujene and thujyl alcohol. 88 However, one species, Orthodon 
linalooliferum Fujita, contains 82 per cent linalool. This compound can be 

88 Naves, "The Formation of the Terpenes in the Labiates," Tech. 2nd. Schweiz. Chem. 
Ztg. 25 (1942), 203. 


converted into many oil components of other species of the same genus. 
Huzita, 89 therefore, considers this linalooliferum plant as the parent species 
of the genus Orthodon. It is, however, equally well possible that the reac- 
tions become blocked at the linalool stage through a mutation process. 

Although the tendency has been to explain the formation of the terpene 
compounds from a Ci precursor like geraniol or citral, it is quite feasible 
that the condensation of the units takes a different and individual path for a 
number of terpenes. We are naturally forced to accept this for irwgalarly 
built compounds such as artemesia ketone and lavandulol, but it might also 
be equally true for a number of the regularly built terpenes, e.g., pinene. 
a-Pinene is one of the most frequently occurring oil constituents, 90 and, 
although the preparation of this ring structure from an aliphatic terpene is 
unknown, easy roads lead from pinene to a number of mono- and bicyclic 
compounds, such as terpineol, borneol, camphene, camphor, fenchone, 
fenchyl alcohol, dipentene, 1,4-cineolc, terpin, pinol, myrtenol, dihydro- 
myrtenol and verbenone (Fig. 2.40). Laboratory experiments may indi- 
cate groups of compounds which can easily be converted into each other, 91 
but we have always to refer to the composition of the natural oils to give 
these groups a physiological meaning. It appears likely that in different 
oils the synthesis of specific compounds (such as limonene) might have 
taken place in several ways such as by ring opening from pineries or ring 
closure of citral, geraniol or other cyclic terpenes, or by even direct synthesis. 

This individuality of many couplings is further supported by our experi- 
ence in the higher terpenes, where often, as in abietic acid, one unit is in an 
irregular position. For an explanation of the different groups of higher 
terpenes, we have to accept formations from single units, single and double 
units, doubling of double units, and doubling of triple and quadruple units. 

Having reviewed all of these theories, let us summarize the established 
facts, in order to draw a conservative conclusion regarding the possible 
synthesis in the plant. We know that : 

1. The structural formula of a large number of the compounds in plants 
can be divided up into branched C& chains. 

2. The arrangement of the branched C 5 units is in most cases a head- 
to-tail union, but exceptions occur in the monoterpene group, and are com- 
mon in sesqui-, di- and triterpenes. 

3. Ring compounds are easily formed from aliphatic terpenes, whereas 
the reverse can only be accomplished with difficulty. 

4. Oxidation, reduction, shifting of double bonds and polymerization 
take place readily. 

89 J. Chem. Soc. Japan 61 (1940), 424. 

90 a-Pinene occurs in 375 oils, according to Ganapathi, Current Sci. 6 (1937), 19. 

91 Okuda, J. Chem. Soc. Japan 61 (1940), 161. 





\ OH 


born col 



iH 2 OH 




fcnchyl alcohol 



Cf-terplneol dipontone 

FIG. 2.40. Tcnxjnc family. 



5. The branched C 6 unit is distinguishable in the formulas of a number of 
nonterpenes coupled with nonbranched structures. 

6. The terpenes are often accompanied with propyl benzene derivatives 
and straight chain hydrocarbons. 

On the basis of these facts, we may safely conclude that a number of 
terpenes are formed from a unit which can give rise to one or more branched 
Cs chains before or after the condensations. It is possible that the (X unit 
is not the actual structure undergoing condensation, and that more complex 
compounds are involved, which split off certain groups aftar condensation 
has taken place. This would include the precursors as described by Hall 
and Emde, viz., phosphoric acid esters as the sugar precursor, and their 
degradation products, and protein complexes carrying the condensing struc- 
tures which release the terpene compounds when formed. The regular 
head-to-tail union may be predetermined in the compound from which the 
terpene is formed, or the mechanism of the condensation may be such that 
this type of union occurs. 

The terpenes already formed readily undergo secondary changes, such 
as reduction, oxidation, esterification and cyclization, and this fact may 
explain the large variety of derivatives of the same pattern. These families 
of terpenes may have their origin in independently formed key terpenes, 
such as gcraniol, citral, pinene, etc. Higher terpenes may have been formed 
through a condensation of lower terpenes of the same or different chain 
length, whereby quite often derivatives from the regular and symmetrical 
architecture can be observed. No indications are available that would 
justify connecting the terpenes directly with other essential oil components, 
such as straight chain hydrocarbons or propyl benzene derivatives. Al- 
though the majority opinion favors a connection through the carbohydrate 
metabolism in the plant, there is no reason to assume that these products 
are formed in the same phase of these processes. 92 - 93 Other essential oil 
components show structural features strongly suggesting connections with 
fat and nitrogen metabolism. From chemical evidence we can draw the 
conclusion that the complexity of the oil composition is caused by excretion 
or secretion of products formed in many metabolic processes taking place in 
the plant. 

Since the volatile oils are intimately connected with vital processes in 
the plant, the presence of these specific components has been used also in 
the determination of the evolutionary status of plant families. 94 

A continued, thorough chemical study of the volatile, and especially of 
the nonvolatile, components will undoubtedly give us a more complete 

92 Simpson, Perfumery Essential Oil Record 14 (1923), 113. 

93 Hall, "Relationships in Phytochemistry," Chem. Rev. 20 (1937), 305. 

94 McNair, Am. J. Botony 21 (1934), 427. Butt. Torrey Botan. Club 62 (1935), 219. 


picture of the processes which take place and of the structures which are 
formed in the metabolic activities of the plant. Although this knowledge 
must be the basis for any speculation on the mechanism involved, we have 
to turn our attention again to the living plant itself in order to collect ex- 
perimental support for our theory of what actually happens. One of the 
ways in which the plant physiologist tries to solve these problems is to study 
the cells in which the oils are deposited, and the circumstances under which 
oil formation takes place 

The observation has been made that some of the cells or spaces in plant 
tissue are filled with oily droplets, difficult to distinguish from fatty oils. 

Courtesy of Dr. J. Enonrd and Mr. S. Orne, Editor. 

ILL. 2.3. Lysigenous oil sac in ftubus rosaefolius Smith. 1 
1 Engard, Univ. Hawaii, Research Publication, No. 21 (1944). 

These oils can be detected by staining with sudan and osmic acid, and a 
distinction from fatty oils is best made by taking advantage of the presence 
of substances with a chemically more active character than the unsaturated 
hydrocarbons and alcohols, i.e., aldehydes and phenols. For example, 
droplets containing phenols can sometimes be stained with phloroglucinol 
hydrochloride. The presence of aldehydes is shown with fuchsin and 
sodium bisulfite reagents. 95 

The oil secretion appears in different cell groups (Illustrations 2.3 and 
2.4), and distinctions have been made between external and internal gland 

95 Czapek, "Biochemic der Pflanzen," Vol. Ill, 593, Drittc Auflage (1925), Vcrlag G. 
Fischer, Jena. 


cells. 96 The external glands are epidermal cells or modifications of these, 
such as the excretion hairs. The secretion product is usually accumulated 
outside the cell between the cuticle and the rest of the cell wall. The cuticle 
is a thin skin covering the secretions and a slight touch suffices to break this 
thin piece of skin. Thus, on touching the plant, we observe immediately 
its well-known scent. 

The internal glands are located throughout the plant; they are fornj xl by 
the deposition of the oils between the walls of the cells. This schism i: cells 
has been called a schizogenous formation. If this is iollowed by dissolution 

Courtesy of Dr. F. M. Turrett and Dr. L. J. Kioto, 
The Botan. (/a*., Vol. 101 (1V40), 86t. 

ILL. 2.4. Tangential section showing oil glands of Washington navel orange fruit. 

of the surrounding cells, morphologists speak of a schizolysogenous gland 
formation. Often these intracellular glands have grown to form long canals, 
coated on the inside with a layer of thin-walled cells. This coating is said 
to have a double function, viz., the separation of other tissues from the oils 
and the formation of oils and resins. The secretion forms in the epithelial 
cells or in the membranes and passes through the cell wall into the interior 
of the gland. The secretion crosses a mucilagenous material produced by 
the outer membranes of the secretion cells which has been called the resinog- 
enous layer by Tschirch. This layer does not possess any of the secretory 
functions ascribed to it, and the designation "resinogenous layer" is in- 

96 Haberlandt, "Physiologische Pflanzen Anatomie," 4776, Aufl. 1924, Verlag Engel- 
mann, Leipzig. Tschirch and Stock, "Die Harze," W35, I, 20 (1933), Verlag Borntriigen, 


applicable, at least in the cases of the Umbellifcrac and Rutaccae studied by 
Gilg and collaborators. 97 

Studies on the number and distribution of the glands show unequal 
distribution. The count of the glandular scales in Mentha species shows that 
the lower surface contains 10-25 scales per sq. mm., the upper surface 1-6 
per sq. mm. Dimensions and number of the scales increased near the large 
vein. 98 

If we search the literature 99 regarding the exact place of formation of 
substances like terpenes, we find that a few disputed observations are avail- 
able, wherein it has been noted that secretion vacuoles suddenly appear in 
the cell, then increase in number and size, while cytoplasm and nucleus 
degenerate. These oil globules appear to be surrounded by a membrane. 
Some observers have seen small droplets of oil, formed in or near the chloro- 
plast, which unite later and form the large oil drops. Others have not 
observed any oil drops at all in the cells, but found the oil in the membrane 
layers adjoining the secretion pockets. 

Certain observations along these lines seem to point toward the region of 
photosynthetic activity, where carbon dioxide is reduced and synthesized 
to carbohydrates. Some support is lent to this thesis by experiments which 
attempt to establish correlations between oil secretion and known meta- 
bolic processes in the plant. Examples of this angle of research are to be 
found in studies on the effect of climatic and growth conditions on oil 

A typical example of such investigations is contained in a report on the 
oil content and composition of Japanese mint (Mentha arvensis) grown in 
the United States, in which it was established that conditions in southeastern 
states do not favor the formation of menthol to the same extent as those in 
the northern and western states. The average differences in large sections 
of America are of the order of 74.5-81.0 per cent for combined menthol. 
Data on the individual oils obtained in the different regions show a spread 
for total menthol of 65.2-88.7 per cent and for combined menthol of 1.7-11.1 
per cent. Sievers and Lowman 100 rightly stress, therefore, the importance 
of a critical attitude toward the evaluation of results obtained in such sur- 
veys. More reliable evidence is obtained when the handling and oil de- 
terminations are carried out under strictly controlled conditions. 

Although such statistical experiments are important from a commercial 
and agricultural point of view, it is difficult to draw any theoretical conclu- 

7 Arch. Pharm. 268 (1930), 7. 

98 Hocking and Edwards, J. Am. Pharm. Assocn. 32 (1943), 225. 

99 Ttmmann, Ber. deut. pharm. Ges. 18 (1908), 491. Czapek, "Biochemie der Pflanzon," 
III (1925), 585. 

100 "Commercial possibilities of Japanese Mint in the United States as a source of na- 
tural menthol," U. S. Dept. Agr. Tech. Butt. 378 (1933), Washington, D. C. 


sions as to the physiological effect of climate, soil and other variables. 
These data, moreover, give an overall picture of the oil content and compo- 
sition of young and old leaves, branches and flowers alike. We know, 
however, that different parts of the plant contain oils which are often of 
very different chemical composition. As an extreme and almost classical 
example, the composition of the oil of Ceylon cinnamon might be given. 
The bark yields oil with a high cinnamic aldehyde content, the leaf oii con- 
sists chiefly of eugenol, and the root oil contains a high percentage of cam- 
phor. Orange and lemon in flowers and fruit contain oils of different com- 
position, and numerous are the examples where only certain parts of the 
plant contain oil: oil of iris, valerian and calamus occur only in the roots; 
sweet birch and cinnamon oils are found in the bark; whereas in the case of 
santalum album and cedar, the core wood contains the valuable oils. 

Better controlled experiments on the influence of climatological condi- 
tions, such as sunlight on the oil formation, are found in a series of articles 
by Charabot and others. 101 Experiments on shaded and unshaded plants 
indicate that light favors formation of oil. 102 ' 103 These observations cover 
a period of several weeks. We possess at least one observation on the daily 
fluctuations recorded on the oii content of nutmeg sage, the oil yield being 
1.5 per cent during the night and in the afternoon only 0.6 per cent. The 
content of esters is highest toward the evening and least at night. The 
yield is lower during windy, dry weather. 104 

To study oil formation as affected by plant development, it is neces- 
sary to select one type of organ and carry out the experiments under rigidly 
controlled and nonvariable external circumstances. Since this is usually 
not feasible, the next best results may be obtained in experiments during a 
stable weather period on fast growing plants, or through the other extreme 
of very long periods on slow growing plants, thereby averaging the effect 
of climatic changes. 

Although no experimental data exist which will satisfy the most rigid 
requirements, the second type of experiment is represented by the analysis 
of oil from the peppermint plant during different stages of growth. Bauer 105 
analyzed the oils of Mcntha pipcrita at four stages before, and during, bud 
formation; and during, and after, flowering. His findings are recalculated 
and summarized in Illustration 2.5, in such a way that the curves represent 
the percentage of the components relative to the fresh weight of the plant. 
The different corresponding growth stages are indicated, I, II, III and IV 

101 Charabot and Hubert, Bull. soc. chim. [3] 31 (1904), 402. 

102 Lubimcnko and Norvikoff, Butt. Appl. Bot. 7 (1014), 697. 

103 Rabak, U. S. DepL Agr., Bur. Plant Ind. Butt. No. 454 (1916). 

104 Gaponenkov and Aleshin, /. Applied Chem. U.S.S.R. 8 (1935), 1049. 

106 Pharm. Zentralhatte 80 (1939), 353. Relation between the composition of peppermint 
oil and the vegetative development and variety of the plant. 


representing the period before budding, during bud formation, flowering 
stage, and after flowering stage. 

The percentage of oil increases until flowering, when it either drops or 
remains constant. This is due chiefly to a decrease in free menthol forma- 
tion, although the ester menthol continues to increase slowly, but steadily, 
probably at the cost of the free menthol. The constitution of the oil of a 
related mint, "Pfalzer mint/' shows the same behavior during development 
in regard to the increase of ester content. Typical for this mint, however, 




Mitcham mint 

Pfalzer mint 






Growth stages 

ILL. 2.5. Percentages of mint oils and their components at various stages of development. 

is the increase in compounds other than the alcohol, probably mcnthone or 
dehydration products. Similar conclusions can be drawn from the in- 
vestigations of Charabot 106 on leaves of Lavandula, Mentha piperita, Ocimum 

lofl Charabot and Laloue, Compt. rend. 147 (1908), 144. Charabot and Gatin, "Le 
Parfum chez la Plante," Paris (1908). Charabot, "Les Principes Odorants des Vegetaux," 
Encycl. Scient., Paris (1912). Charabot, Am. J. Pharm. 85 (1913), 550. Charabot, Compt. 
rend. 129 (1899), 728; 130 (1900), 257, 518, 923. Charabot, Butt. soc. chim. [3] 23 (1900), 
189. Charabot, Ann. chim. phys. [7] 21 (1900), 207. Charabot and H6bert, Compt. rend. 
132 (1901), 159; 133 (1901), 390. Charabot and H6bcrt, Butt. soc. chim. [3] 25 (1901), 
884, 955. Charabot and Hubert, Compt. rend. 134 (1902), 181; 136 (1903), 1678. Chara- 
bot and Laloue, Ibid. 136 (1903), 1467. Charabot and Hubert, Butt. soc. chim. [3] 29 (1903), 
838. Charabot and Hubert, Compt. rend. 138 (1904), 380. Charabot and Lalouo, ibid., 
1513. Charabot and Hubert, Ann. chim. phys. [8] 1 (1904), 362. Charabot and H6bert, 
Compt. rend. 139 (1904), 608. Charabot and Laloue, ibid. IZ9 (1904), 928; 140 (1905), 667. 
Charabot and Herbert, ibid. 141 (1905), 772. Charabot and Laloue, ibid. 144 (1907), 152. 
Charabot and Laloue, Butt. soc. chim. [4] 1 (1907), 1032. Charabot and Laloue, Compt. 
rend. 144 (1907), 152, 435. Charabot and Laloue, ibid. 142 (1906), 798. Charabot and 



basilicum, Verbena tryphylla, Artemisia absinthium and Pelargonium. In 
the later stages of growth the alcohols decrease probably at least partly 
through ester formation and dehydration to hydrocarbons. This process 
in turn is followed by oxidative reactions wherein aldehydes and ketones 
are formed. A decrease in oil content of the leaves during flowering has 
been observed by Charabot et al. on Verbena tryphylla. 107 In Table 2.1 

TABLE 2.1. Mo. OF OIL IN PARTS OF Verbena tryphylla PER WHOLE PLANT 



After Flowering 











I weaves 










Weight of Plant 

366 K . 

259 g. 

is listed the mg. oil present in different parts of the plant, during the flower- 
ing, and after the flowering period. In this period the leaves lost a consider- 
able amount of oil, as compared with other parts of the plant. Analysis of 
the flower oil showed that the material lost from the flower consisted chiefly 
of citral. Charabot attributed this decrease in oil content of the leaves in 
Verbena and Artemisia absinthium 1 "* to a consumption of the oil constituents 
by the flowers, and postulated, therefore, a flow of oil from the leaves to the 
flowering parts. 

When we take into account the way the oils are stored in the plant, and 
their toxic action when released, this transfer seems unlikely. It is, how- 
ever, possible that material which otherwise would have contributed to the 
formation of the oils is used up in the flowering stage, and that the reduced 
formation of oil is unable to compensate for the constant loss through evap- 
oration. The same explanations can be made for Oharabot's experiment in 
which it was shown that Mentha pipcrita 10 * and Ocimum basilicum 110 plants, 

Lalouo, Bull. soc. chim. [3] 35 (1906), 912. 

Similar results are recorded by Rabak, J. Am. Chem. Soc. 33 (1911), 1242. Nylov, 
J. Gov. Bot. Garden Nikita Yalta Crimea 20 (1929), 3. Repts. Schimmel & Co., 1926, 141, 
142, 143. Spiridonova, /. Gen. Chem. U.S.S.R. 6 (1936), 1536. 

Experiments on salvia seedlings are recorded by Wyslling and Blank, Verh. Schweizer 
Naturf. Ges. Locarno (1940), 163. 

Data on oil content at different stages recorded by Francesconi, Gazz. chim. Hal. 49, I 
(1911), 395. Francesconi and Sernagiotto, Atti accad. Lincei 20, II (1911), 111, 190, 230, 
249, 255, 318, 383. 

Data on camphor tree recorded by Hood, /. Ind. Eng. Chem. 9 (1917), 552. 

107 Charabot and Laloue, Bull. soc. chim. [4] 1 (1907), 640, 1032. 

108 Charabot and Lalouo, Compt. rend. 144 (1907), 152, 435. 
108 Charabot and Hubert, Bull. soc. chim. [3] 31 (1904), 402. 
>" Charabot and H6bert, ibid. [3] 33 (1905), 1121. 


after debudding, contain more oil in the leaves than under ordinary cir- 

Long-term experiments stretching over two years, and averaging the 
climatic influences, have been carried out by Charabot and Laloue on Citrus 
aurantium. From their extensive data, the total oil present in a twig with 
an attached leaf can be followed through its development. Illustration 2.0 
shows clearly the large increase in absolute weight of the oil during the early 



Branch oil 

May June May May 

ILL. 2.6. Total oil content in growing leaf and branch of Citrus Aurantium. 

period of growth. During the later period the formation in the branches is 
not even intense enough to compensate for the losses, due to consumption, 
transportation to other parts 111 and evaporation. An increased production 
of limonene is observed. This is probably formed by the dehydration of the 
initially present, free and esterified linalool and geraniol. Similar experi- 
ments on the oil content at different stages of development were carried out 
on the oil of bergamot. A tendency in the expected direction was actually 
observed, i.e., an increase of esters and an increase of terpenes, through the 
loss of water and through cyclization. 

111 Charabot and Laloue, Compt. rend. 142 (1906), 798. Butt. soc. chim. 35 (1906), 912. 
Hood, J. Ind. Eng. Chem. 8 (1916), 709; 9 (1917), 552. Laloue, BuU. soc. chim. [4] 7 (1910), 
1101, 1107. 


The essential oils extracted from the trunk of the young Chamaecyparis 
formosana tree contain a large amount of d-myrtenol and smaller amounts 
of d-a- and /3-pinene. d-Dihydromyrtenol, which is only present in very 
small amounts in the young tree, is a major constituent of the older tree. 
The simultaneous disappearance of the pinenes and myrtenol strongly sug- 
gests that the tree converts these substances into the characteristic and rare 
alcohol, dihydromyrtenol, by oxidation and reduction processes 112 (Fig. 2 41). 

A fourth method for the determi- 
nation of the effect of growth on the | <pH*OH <pH 2 OH 
oil content consists of the comparison 
of the analysis of the oils of leaves 
harvested at the same time, but re- 
presenting different developmental 
states. The influence of preceding 
variations in weather conditions on ln . n _ . , . , ^ , 

a-pinene myrtenol dihydromyrtenol 

the older loaves has to be reduced in _, ... _ , . ,. ,. _ 

. .. . A . . riG. 2.41. Related Im'vrhc Terpencs in 

a way similar to that mentioned pre- Chamaccypans formosana. 

viously in describing experimental 

methods. It has been shown of peppermint oil that the percentage of yield 
decreases from the upper to the lower leaves. In agreement with the find- 
ings of Charabot and others, Xilov and Ponta 113 found the ester and oxygen 
content higher in the older leaves. The ester content is also increased 
through the effect of hydrogen sulfidc or ethylene. 

The same gradient in oil content is seen in Pogostemon patchouli, 11 * where 
the oil is chiefly located in the upper three pairs of leaves, confirming the 
general rule that the production of the oil coincides with the most active 

If we want to study the influence of different environmental factors on 
oil formation, it appears from the preceding discussion that we have to choose 
plant material of the same physiological age. It is also advisable to study 
the oil composition of young tissues which, duo to their intense synthesis, 
are bettor suited to reflect any effects of the environment. 

Careful studies in this direction have boon made by Berry et al. 115 on 
the oil of Eucalyptus cncorifolia. The oil of this eucalyptus consists chiefly 
of cineolo, the hydrocarbons pinene and Z-0-phellandrene, the carbonyl 
compounds Z-phellandral, cuminal, cryptal, M-isopropyl-A 2 -cyclohexene- 
1-one; also present are J-a-phellandrene and some alcohols such as australol. 

112 Sebe, ./. Chem. Soc. Japan 62 (1941), 22. 

118 Trudy Vsesoyuz, Nauch.-l ssledovatel. Inst. Efirno Ufasl. Prom. Sbornik Rabot Perechnoi 
Myate, No. 5 (1939), 104. 

4 do Jong, Her. trav. chim. 30 (1911), 211. 
*,/. Chem. Soc. (1937), 1443. 


Although no marked change in the composition or in the amount of oil 
can be noted in the mature leaves, the case is quite different in the younger 
stages of development. The total oil content and the amount of the differ- 
ent components from the growing tips of the branches at different times of 
the year are shown in Illustration 2.7, expressed in percentage of the wet 
weight of the plant. 

\ p - t Aldehydes ^ 

Summer . Autumn Winter Spring Summer 
ILL. 2.7. Composition of oil from growing tips of Eucalyptus cnconfolia. 

It is thus possible to show the absolute formation of each group of ter- 
penes per unit weight of the plant, uninfluenced by an increased synthesis 
of one of the components, as would be the case if we expressed the composi- 
tion as a percentage of the oil. The amount of alcohols formed at different 
periods does not seem to be greatly affected. More aldehydes are formed in 
autumn than in spring. During the period of maximum growth in spring 
and summer the formation of oil is highest. This increase cannot be 
attributed to a greater production of alcohols and aldehydes, because the 
alcohol content at different periods is not greatly affected; and in the case of 
the aldehydes we notice even the opposite effect: a decrease during spring. 
The real contributors toward the increased oil production are the tcrpene 
hydrocarbons, viz., /3-phellandrene and cymene, and in a lesser degree the 



berpene-oxide cincolc. From analytical data on mature leaves, it is known 
that the phellandrene content of the oil is greatly reduced, and that the 
symene content was only 3-4 per cent, as compared to 19 per cent in the 
Doling leaves. From these analyses Berry concludes that a- and /3-phellan- 

!-i80piopylcjclobcxen-2-one-l oj.phellandrene jxymene 

FIG. 2.42. Relations between Terpcnes in Eucalyptus cneorifolia. 

1 Wallaoh, Liebigs Ann. 340 (1905), 1; 343 (1905), 35. 

2 Borgwardt and Schwenk, J. Am. Chem. Soc. 56 (1934), 1185. 

3 Stephens, J. Am. Chem. Soc. 48 (1926), 1824. 

drene might be the precursor of certain terpenes, such as p-cymene, phel- 
landral, cuminal and 4-isopropylcyclohexene-2-one-l. In the laboratory 
these conversions can be carried out with great ease 116 - 117 - 118 (Fig. 2.42). 
The optically active compounds present in this oil are stereochemically 

118 Borgwardt and Schwenk, /. Am. Chem. Soc. 56 (1934), 1185. 

117 Stephens, /. Am. Chem. Soc. 48 (1926), 1824. 

" Wallach, Liebigs Ann. 340 (1905), 1; 343 (1905), 35. 


related and belong to the laevorotatory series, constituting additional 
evidence of their common genesis. A similar relationship for c/-phellandrenc 
has been noted by Berry 119 in Phellandria aquatica, viz., d-a- and d-/3-phel- 
landrene and the corresponding d-ketone. 

Many more observations made on the yield and composition of plants 
grown under different conditions of soil, climate and treatment, and in 
different stages of development could be added, but most of these are of 
such a specific and often experimentally vague nature that they can justify 
only the general conclusion that the more actively the plant grows, the larger 
the quantity of oil formed. 

To gain a deeper insight into the physiological processes involved in 
formation of essential oils, \ve have to limit our experimental subjects to 
well-defined organs of well-defined species of plants. The experimental 
work on the composition of the eucalyptus group is a warning that the oils 
from closely related species may be widely different. Even species indis- 
tinguishable by ordinary morphological techniques can be distinguished on 
the basis of the production of oils of different chemical composition. 120 

In many cases, the abnormal behavior is due to hybridization of different 
apecies. Extensive genetic work has been carried out by Russian workers, 
and has led to the conclusion that considerable changes in the synthetic; 
activity of the plants can be observed under the influence of hybridization, 
so that compounds may appear in the oil which were not present in the 
parent plants. 15 * 1 On the other hand, Mirov in his investigations on the 
turpentine from the genus Pinus describes a Ponderosa-Jeffrey hybrid 
which contains ter penes inherited from the Ponderosa parent, and heptane 
from the Jeffrey parent. 122 - 123 

Polyploidy and other types of mutations, such as hetoroploidy and 
chromosome aberration, may cause changes in the quantity and composi- 
tion of the oils, as has been demonstrated in Pelargonium roseum. 121 

Many factors are, therefore, involved which change the composition of 
the oils ; and for a successful study of these effects and the solutions of prob- 
lems of oil formation it is imperative not to add further complications, such 

" 9 Berry, Killen, Macbeth and Swanson, J. Chem. Soc. (1937), 1448. 

120 Foote and Matthews, /. Am. Pharm. Assam. 31 (1042), 65. Pen fold and Morrison, 
J. Roy. Soc. N. S. Wales [I] 69 (1935), 111; [II] 71 (1938), 375; [III] 74 (1941), 277. 

121 Snegirev, Bull. Appl. Bot., Genetics, Plant Breeding U.S.S.R., Ser. Ill, no. 15 
(1936), 245. Nilov, Nesterenko and Mikhel'son, Biokhim. i Fiziol. Drevesnykh i Kus- 
tarnykh Yuzhnykh Porod 21, no. 2 (1939), 3. Knishevetskaya, Trudy Gosudarst. Nikitskogo 
Botan. Soda 21, no. 2 (1939), 29. 

Mirov, J. Forestry 27 (1929), 13; 30 (1932;, 93; 44 (1946), 13. 

123 Kurth, "The Extraneous Components of Wood," "Wood Chemistry," edited by L. 
E. Wise (1944), 385. 

124 Urinson, Bull Appl. Bot., Genetics, Plant Breeding U.S.S.R., Ser. Ill, no. 13 (1936), 


as are caused by drying, distilling and harvesting procedures. Storage for 
a few hours even in the shade may in special cases cause a considerable de- 
crease in the oil content. Russian workers found for nutmeg sage that its 
volatile oil content decreases 33 per cent after storage for 3 hr., and 55 per 
cent after 6 hr. in the shade, while in the sun it decreases 62 per rent after 
6 hr. Their conclusion in this case is that the material should be collected 
at night and immediately distilled. 125 The losses in volatile components 
from intact plants are well known and have been measured quantitatively 
through micro combustion. The number of excreted products is consider- 
able. These results 126 serve as a warning that external circumstances may 
easily modify quantity and quality of oils, with the result that changes due 
to other variables cannot be distinguished. On exposure to air, and es- 
pecially to sunlight during drying of the plant material in the fields, a con- 
siderable amount of volatile oil may be lost by oxidation, polymerization 
and resinification. 

For practical purposes, certain compromises have to be made; neverthe- 
less it should be our goal to choose conditions and experimental material 
so carefully that reproducibility is assured, and the many factors involved 
can be changed individually. Only in such a way can we expect to unravel 
the fate of the plant metabolites secreted as essential oils. Such experi- 
ments might well throw light on another intriguing problem, i.e., the func- 
tion of the essential oil in the plant. 

A discussion of this subject invites a look at plant metabolism from a 
more general viewpoint. 


When the plant organism is alive and in process of development, external 
substances are constantly absorbed and transformed into "building stones. " 
This reshaping of the foreign substances and their incorporation into the 
plant system, known as assimilation, requires energy, which is obtained by 
a series of reactions, whereby a part of the assimilated products is oxidized. 
The balance of these two series of reactions appears in the growth of the 
plant. Therefore, while some of the plant material is in a continuous flux, 
undergoing degradation and rebuilding, another important part of the reac- 
tion products can be expected not to take part in an uninterrupted chain 
of reactions. 

Some of these products such as cellulose will be deposited in cell walls, 
the plant thereby acquiring a more rigid structure. Other substances 
such as starch are stored as energy and organic material sources, to be 
drawn upon when circumstances arise which cause the re-entrance of these 

126 Gaponenkov and Alcshin, /. Applied Chem. U.S.S.R. 8 (1935), 1049. 
126 Haagen-Smit, unpublished results. 


substances into the reaction chain. We can thus assign a certain function 
in the plant to these particular compounds; but we find it much more difficult 
to do this with a number of other substances, such as alkaloids, anthocy- 
anins and flavones, essential oils, resins and rubber latex. 

It is a well-known fact that some plants emanate, besides carbon dioxide, 
a considerable amount of organic material, chiefly the carriers of the smell 
of the plant. In some rare cases so much oil is excreted that the oil can be 
set afire, as in Ruta graveolens and Dictamnus. At the same time, relatively 
large amounts of these essential oils are deposited in the plant, and our only 
evidence for the assumption that such compounds are unimportant sources 
of energy to the plant is the fact that, prior to leaf abscission, the oils are not 
transferred to the stem, as is the case with a large part of the carbohydrates. 

The question has, therefore, repeatedly been asked: Does the plant 
derive any specific benefit from these oils? 127 Opinions in this field are based 
on the observations that some oil-bearing plants are attractive to certain 
animals, whereas others are repellent. In individual cases, therefore, a 
contribution is made toward more effective pollination through insect 
visits. 128 In a number of other cases a degree of protection against the 
depredations of animal 129 and plant 130 parasites may be afforded by the 
irritating effect of many oils. Some observers maintain that the oils func- 
tion as reserve food, as a means of sealing wounds, or as a varnish to prevent 
excessive evaporation of water (cell fluid). These opinions are not beyond 
question, and do not appear to be supported by experimental evidence often 
having their origin merely in a teleological approach to the subject. Most 
investigators, including Tschirch, the famous resin chemist, hold the view 
that the functions attributed to those substances are more often of acci- 
dental, than of essential, importance to the plant. Those who consider 
these products a result of phenomena accompanying the growth process 
have used the term "waste product." This, however, rather underrates the 
value of these secretion products, which, through their formation, may 
contribute to syntheses important in the continued existence of the plant. 
Some carbohydrate precursors may serve as hydrogen acceptors, and in 
doing so may become unusable for further synthesis. Their function, 
therefore, may arise in their formation, and not in a later stage. Thus we 
might compare the oils to "Hobelspane," the shavings of a plane. As 
reason for their disposal, the opinion has been expressed that substances 
such as terpenes, mostly hydrocarbons, are so far remote in their chemical 

127 Czapek, "Biochemie dcr Pflanzen." Ill Auflage, G. Fischer, Jena (1925). Dctto, 
Flora 92 (1903), 146. Gerhardt, Naturwiss. 8 (1920), 41. 

12 v. Frisch, Verh. Zool. Bot. Ges. Wien 65 (1915), 1;.$8 U918), 129. 

129 Stable, "Pflanzen und Schnecken," Zeitsch. Natur. Medicine 22, NFXV, Jena. 
Preycr, Flora 103 (1911), 441. Haberlandt, "Physiologische Pflanzenanatomie," 4 Aufl. 

130 Verschaffeit, Kgl Ak. Amsterdam (1910), 536. Gertz, Jahr. Wis. Bot. 56 (1915), 123. 


and physicochemical conduct from the properties of the living substances 
that they are excreted as "korpcrfremde" or alien materials. 

There are others Avho refuse to believe in the waste product origin of the 
essential oils, and Lutz suspects that these oils have constituents which can 
be hydrogen donors in oxido-reduction reactions. Although they are 
thereby transformed into neutral compounds as far as catalysis is concerned, 
they might re-enter the reaction scheme through a reduction in the presence 
of light. To prove this theory, experiments were carried out on a fuLgus 
belonging to the Hymenomycetes on which Lutz deternrned the antioxidant 
or hydrogen-donor action of oil constituents. Phenols were found to be 
excellent donors, as is well known from the investigations of Moureu, but 
secondary and tertiary alcohols and aldehydes also showed strong activity. 
Hydrocarbons are inactive in the dark, but become active in the light. On 
the other hand, primary alcohols, terpene oxides like cineole, and ketones 
are inactive, and perhaps are from this viewpoint the real waste products. 
Lutz 131 considers the oil components as moderators in intracellular oxidation 
to protect against the action of atmospheric agents. He also includes the 
possibility that some of the components may be used as an energy source 
during a deficiency state caused by an interruption of the normal assimila- 
tion of carbon dioxide 

It has also been suggested that plants which emanate a considerable 
arnount of oils are prevented from becoming too warm since heat is absorbed 
in the vaporization of the oils. In this way the oils w r ould function as a 
water-sparing mechanism. However, measurements of the relatively large 
amounts of water and small amounts of oil involved, show clearly that such 
a contribution would be negligible. In the search for some useful function 
for the terpenes, Teodoresco 132 was one of the few who carried out experi- 
ments on the effects of oils on plants. He showed that the absorption of 
sun radiation by the essential oil atmosphere around the plant was negligible 
and certainly did not have any influence on the water evaporation. This 
oft-debated point, based on a misinterpretation of TyndalPs work, was 
solved by admitting oil vapor around the plant without, however, making 
direct contact, and determining the loss of weight through transpiration. 
Neither direct weighing of the loss of water, as shown in Illustration 2.8, 
nor transpiration measurements with a potometer demonstrated any heat- 
screening effect. If, however, the oil was allowed to come in contact with 
the plant, a considerable reduction in transpiration was evident. Although 
the damaging effect of prolonged exposure to the oils had been observed 
before, Teodoresco showed that when the vapor is removed soon enough, 
recovery follows in a few hours. This action is not confined to the oils 

181 BuU. soc. chim. biol. 22 (1940), 497. 

i Audus and Cheetham, Ann. Botany (N.S.) 4 (1940), 465. 


obtained from the same plant, but is a more or less nonspecific effect for the 
volatile oils in general. 

It would, therefore, appear that a number of essential oils exercise di- 
rectly or indirectly a definite action on the transpiration in plants. How- 
ever, experiments carried out on partial saturation of the atmosphere sur- 


t nB f 

Rosemary Rosemary 
f in A f mB f 

Noon Midnight Noon 

ILL. 2.8. Vapor of Rosmarinus officinalis on Dracocephalum moltlavica. 1 

l Teodoresco, Rev. gen. boian. 35 (1923), 382. Refutations also by Gnjns, Arch, 
neerland. physiol. 3 (1919), 377. Detto, Flora 92 (1903), 147. Xicol, Compt. rend. 489 
(1929) 289; Biochem. J. 26 (1932), 658. 

rounding the plant, simulating more closely the outside conditions, showed 
that the concentration of essential oil vapor would rarely be high enough 
to cause any significant decrease in transpiration. 

The oils inside the plant, although enclosed by special tissues, might 
have an influence on the transpiration and other important functions of the 
plant rather than the vapor of the excreted oil, since there is reason to be- 
lieve that cell walls would not be an insurmountable obstacle for the oil. 
This effect would result in a general retardation of a number of the plant 
activities. Teodoresco mentions specifically a decrease in the nyc*4nastic, 


seismonastic, phototropic and gcotropic movements. The oils inhibit also 
the formation of chlorophyll in etiolated plants when exposed to light, and 
cause a decrease in permeability. Continued exposure to the oil vapors 
causes damage to the living substance, producing a greater permeability, 
which is in turn followed by death. 133 - 134 - 135 General toxic action on plants 
has been observed by Bokorny 136 with oil of turpentine in concentration of 
1 : 50,000. 

The action of some essential oils is similar in certain respects to $iat of 
anaesthetics on animal cells. This problem of anaesthesia is one of the 
fundamental problems in general physiology, and the results obtained in 
these studies might well contribute to the understanding of similar effects 
in plants. The first effect of fat solvents, narcotics and stimulating agents 
is identical, 137 and it may be assumed that they cause a reversible lowering 
of the permeability for water and water-soluble substances, in harmony 
with the findings of Teodoresco and others on the pronounced inhibition of 
transpiration in plants. 

The inhibiting and damaging effect of the oils on many life processes 
has been turned to our advantage in the use of these compounds as bac- 
tericidal and fungicidal agents. However, from the diversity of the com- 
pounds in essential oils, it is clear that we have to regard with suspicion 
any general statement on the bactericidal action of the essential oils. From 
specific cases which have been studied, it can be concluded that the terpene 
derivatives, while possessing action bactericidal to certain organisms, are 
not able to inhibit growth in all of the numerous types of microorganisms. 
It is, therefore, not astonishing to see aqueous infusions of, for example, 
lavender, peppermint and juniper drugs fall victim to putrefaction after 
several days of standing. 138 

On account of their bactericidal action, a number of volatile oils have 
been employed in the past for the treatment of urogenital infections. The 
simultaneous irritating effect on animal tissue applied in measured degree 
may stimulate repairs of tissue, and assist in the removal of mucous from 
trachea and bronchia and relieve tension of the stomach and colic. 

Other toxic effects are reported on cultures of fibroblasts, and further 
examples of their inhibitory effect on life processes can be seen in the an- 
thelmintic effect of different oils, especially chenopodium oil. The effect 

33 Burgerstein, Verhandl Zool. Bot. Ges., Wien, 1884. 

34 Heller, Flora (1904), 1. 

35 Vandervelde, Chem. Zentr. I (1900), 481; II (1901), 440. 

36 Pflag. Arch. 72 (1899), 555. 

37 Heilbron, "An Outline of General Physiology," 37 (1938), 437. Davson and Danielli, 
"The Permeability of Natural Membranes," (1944). 

188 Kliewe and Hutmacher, Dent. Apoth. Ztg. 53 (1938), 952. DC Potter, Compt. rend. 
8oc. 6ifti 131 (1939), 158. 


)f this American wormseed oil on round worms, hookworms and intestinal 
imoebas is very similar to that of santonine, a sesquiterpene lactone present 
n Semen cinae. The toxicity of these oils for certain organisms cannot be 
neasured simply by their bactericidal action. Thymol, for example, is 
nuch stronger antiseptically but is much less active as an anthelmintic than 
jantonine or ascaridole, the active components of wormseed oil. The 
}oxic effect of some essential oils and oil components is not limited to the 
organisms which have to be destroyed, and excessive use in higher animals 
ind man causes depression of the higher centers followed by convulsions. 
\ few cases are known where an apparent stimulating effect is observed. 
This is the case with terpene compounds such as camphor and menthol, 
vhich are used as circulatory stimulants in cases of collapse. It is assumed 
/hat when the action of the heart muscle is depressed, camphor may im- 
Drove the cardiac condition and remove arrhythmia. 

On the basis of recent investigations, these effects seem also to be due to 
in inhibitory action on nerve fibers which counteract other fibers belonging 
,o the sympathetic nervous system. Through this effect on the inhibitors, 
sertain muscles are stimulated. A similar explanation might well hold 
'or the acceleration and strengthening of the peristaltic movements of the 
imall intestines of rabbits, according to Haffner, 139 and Sone and Shiro. 140 

In general, we observe a definite toxic effect on the important life proc- 
esses, and excessive doses, because of depression and paralysis of the central 
lervous system, are followed by death. The essential oils probably inter- 
ere with delicate mechanisms, through their chemical and physical eiiects, 
either by entering and disturbing colloidal systems or by taking part in 
jertain reactions. The oils themselves are at the same time exposed to 
nany influences, which may change them in such a way that removal 
trough the kidneys is possible. This so-called detoxication process takes 
nany forms, and may consist of esterification, oxidation, reduction, or 
jonjugation with compounds such as glycuronic acid and amino acids. 
When borneol is fed to dogs, it appears as glycuronide in the urine; when 
/anillin is ingested, oxidative processes are responsible for the excretion of 
fanillic acid. A combination of both processes is evident when camphor is 
amoved in oxidized form. When such a removal is not possible, as, for 
example, by accumulation of the oils through injection, the organisms react 
Dy walling off the foreign material and tumors and sterile abscesses are 
reported. 141 

This reaction is in principle similar to what happens in a plant lacking 
;he elaborate detoxication and excretion mechanisms present in the higher 

138 Arch, exptl. Path. Pharmakol. 186 (1937), 621. 

140 Tfihoku J. exptl. Med. 30 (1937), 540. 

141 Saito, Folia PharmacoL, Japan 23 (Breviaria 2) (1936), 6. 


animals. A considerable part of the metabolites which are not immediately 
taken up in further reactions or are not removed by evaporation will have to 
remain in or near the secretion cells. The interfering action of the oils may 
then cause lysis of the surrounding cells and changes in the normal metabo- 
lism, resulting in the formation of cork and mucilagenous layers, with low 
permeability for the oil. We may safely conclude that once removed from 
the continuous chain of reactions, these compounds are a potential danger 
to all living tissues, and both plant and animal react by walling off the oil 
from the other tissues. If this is not possible, reactions will take place 
until the compounds are so transformed that they can be excreted, or until 
they have become harmless from the point of view of the surrounding tissue. 

From a general viewpoint, essential oils, alkaloids, resins, rubber, antho- 
cyanins and many other secreted substances may have in principle a similar 
history. Their precursors, linked with essential processes in the organism, 
undergo secondary and further changes when exposed to the medium in 
which they are left behind. 

Due to their commercial importance, our chemical knowledge of these 
end products exceeds by far our knowledge of the processes from which they 
have boon derived. It is hoped that more fundamental studies are being 
carried out in this direction which, in turn, will lead to our more rigid control 
over their formation in the plant. 


Gildemeister and Hoffman, "Die atherischen Ole," 3d Ed. Vols. I, II and III, 
Leipzig (1928-1931). 

Simonscn, "The Terpenes," Vols. I and II, Cambridge (1931-1932). 

Tschiroh, "Die Harzc und die Harzbehalter," 2d Ed., Leipzig (1936). 

Wallach, "Terpcne und Camphor," 2<1 Ed., .Leipzig, 1914. 

Klein, "Handbuch der Pflanzenanalyse," Wien, 1932. 

Scmmler, "Die atherischen Ole nach ihrcn chemischen Bestandteilen," 
Leipzig, 1906-1907. 






Note. All temperatures in this book are given in degrees 
centigrade unless otherwise noted. 



Introduction. The majority of essential oils have alwaj^s been obtained 
by steam distillation or, in the more general sense, by hydrodistillation. 1 
The practical problems connected with distillation of aromatic plants are, 
therefore, of utmost importance to the actual producer of essential oils. 
Yet our present-day technical literature, especially English literature, is 
surprisingly meager in regard to data and information which might serve as 
a really practical and reliable guide. This shortcoming has been felt 
severely, especially during the years of World War II, when prospective 
producers in North, Central and South America sought advice concerning 
the distillation of oils which, due to war conditions, could no longer be 
imported from Europe and Asia. Encouraged by countless inquiries from 
almost every part of the Western Hemisphere, the author finally decided to 
compile a comprehensive paper on this topic which would incorporate not 
only his own experience of many years in the field, but also the most im- 
portant phases gathered from the literature published so far. There exist 
on this subject two really outstanding books, viz., the classical work of Dr. 
von Rechenberg, who spent a lifetime in the actual distillation of essential 
oils and on systematic research pertaining to the physical phenomena and 
laws underlying distillation. These works have never been translated from 
their German text, are now out of print and, due to the ravages of World 
War II, not readily available. This author would consider it an irreplace- 
able loss to our industries if the most important parts of these books, at 
least those dealing with the practical aspects of essential oil distillation, 
were not preserved for posterity. Unfortunately, the lucid writings of 
Professor von Rechenberg have not attained sufficient attention outside of 
Germany. In more than one way they are so fundamental and exact that 
they require no modification. This author has, therefore, translated parts 
of von Rechenberg's treatises, with a view to incorporating some of the most 
essential features into his own text. These books are recommended: 

C. von Rechenberg, "Theorie der Gewinnung und Trennung der atheri- 
schen Ole," Schimmei & Co., Miltitz bei Leipzig, 1910. 

This chapter by Ernest Guenther. 

1 The term "hydrodistillation" is used by von Rechenberg as referring to distillation 
with water vapors (steam). 


C. von Rechenberg, "Einfache und Fraktionierte Destination in Theorie 
und Praxis/' Schimmel & Co., Miltitz bei Leipzig, 1923. 

A much smaller book, "Die Fabrikation und Verarbeitung von atheri- 
schen Olen," by Max Folsch, Hartleben's Verlag, Wien und Leipzig, 1930, 
leans on von Rechenberg's text but adds much practical advice. 

Those interested particularly in the distillation of colonial oils and in 
field distillation requiring simple apparatus are referred to Gattefosse's 
"Distillation des Plantes Aromatiques," Librarie Centrale des Sciences, 
Paris, 1926. 

"Aspects of the Theory of Distillation as Applied to Essential Oils," 
have been described by Leslie Bloomfield in a series of comprehensive papers 
which appeared in the Perfumery and Essential Oil Record, Vol. 27 (1936), 
131, 177, 294, 334, 368, 404, 443, 483; Vol. 28 (1937), 24, 59. 

"A Treatise on Distillation," by Thos. H. Durrans, was published also in 
the Perfumery and Essential Oil Record, June, 1920, 154 to 198. 

The mathematical and physical principles connected w r ith steam distilla- 
tion in general are discussed in "Wasserdampf-destillation," by N. Schoorl, 
which appeared in Rec. Trav. Chim. 62 (1943), 341-379. 

This chapter will be divided into two parts, the first dealing with the 
fundamental or theoretical principles underlying all distillation processes, 
and the second treating more specifically the practical aspects of distilla- 
tion as applied directly in the essential oil industry. 


Essential, volatile or ethereal oils are mixtures composed of volatile, 
liquid and solid compounds which vary widely in regard to their composition 
and boiling points. Every substance with a de terminable boiling point is 
volatile and possesses a definite vapor pressure, which depends upon the 
prevailing temperature, and which is very low in the case of very high boiling 
substances. Hence, the intensity of an odor may be considered, to a certain 
extent and with many exceptions, as a manifestation of the volatility (boil- 
ing point and vapor pressure) of the substance which emits the odor. 

Distillation may be defined as "the separation of the components of a 
mixture of two or more liquids by virtue of the difference in their vapor pres- 
sure" (Stephen Miall, "A New Dictionary of Chemistry/' London, Long- 
mans Green, 1940). The process of distillation is obviously of considerable 
importance to the essential oil producer. There are two general types to 
be considered : 

1. Distillation of mixtures of liquids which are not miscible, and hence 
form two phases. Practically, this applies to the rectification and f ractiona- 
tion of essential oils with steam, and, what is much more important, to the 


isolation of volatile oils from aromatic plants with steam. Distillation with 
steam may also be called hydrodistillation, which general term implies that 
distillation may be carried out either by boiling the plant material or the 
essential oil with water, and creating the necessary steam within the still, 
or by introducing into the retort live steam generated hi a separate steam 

2. Distillation of liquids which are completely miscible in each/ other, 
and therefore form only one phase. Practically, this applies to the rectifica*- 
tion and separation of an essential oil into several fractions (fractionation)," 
without the use of steam. 

The difference between the behavior of single-phase mixtures and two- 
phase mixtures can best be understood by considering what happens when a 
liquid vaporizes, especially on boiling. Let us consider first the case of a 
pure liquid in a closed container. At a given, fixed temperature, the average 
energy of the molecules is fixed. The molecules are in constant and com- 
pletely random motion. Any molecule in the main body of the liquid can 
travel only a short distance before it comes under the influence of other 
molecules at which moment its direction of motion is changed. Any mole- 
cule in the surface layer, however, which happens to be moving in a direction 
away from the main body of the liquid can escape into the space above the 
liquid, thus becoming a vapor molecule. Now, the vapor molecules, too, 
are in constant motion, the speed of the molecules of any kind being de- 
termined solely by the prevailing temperature. Any vapor molecule hitting 
the liquid surface has a chance of being captured by the liquid in other 
words of being reliquefied (condensed). As the temperature is raised the 
number of vapor molecules increases. Obviously the chances of a molecule 
returning into the liquid also increase, so that after a short time the number 
of molecules vaporizing in a unit of time exactly equals the number condens- 
ing (being reliquefied) in the same time. Thus, there arises a condition of 
dynamic equilibrium, with the total number of molecules in the vapor state 
remaining constant. If the space filled with saturated vapors is opened, 
vapor escapes and will be replaced by the same number of molecules, i.e., 
by the same quantity of vapor newly developed from the liquid mass. 
This applies not only to liquids but to solids, because, as pointed out above, 
every substance with a determinable boiling point is volatile. 

Let us now suppose that, still at constant temperature, a second liquid, 
completely miscible with the first one, is added. Since the two liquids 
form a single phase, the surface of the liquid mixture consists only partially 
of molecules of the first kind. The number of molecules of the first kind 
escaping into the vapor space per unit time must certainly depend on the 
number present in the surface layer, and will, therefore, be smaller now 
than it was for the pure liquid. However, the molecules being completely 


miscible, the total number returning from the vapor to the liquid will not 
immediately be changed. Since the total amount of surface is unchanged 
and since now more molecules of the first kind are condensing than are 
being vaporized, temporarily the equilibrium originally established will be 
disturbed. This process continues until a new equilibrium is established, 
when these rates again become equal, and this in turn causes a decrease in 
the number of molecules of the first kind present in the vapor phase at any 
one time. Exactly the same law applies to the second component of the 
mixture. In general, the number of molecules of any component of a 
homogeneous mixture present in the vapor phase will thus be smaller than 
the number present in the same vapor space if the pure liquid is involved. 
The fraction of the surface occupied by either liquid is, of course, propor- 
tional to its relative amount, and consequently the extent to which the rate 
of vaporization decreases will depend on the composition of the liquid. 
The vapor composition of a one phase mixture will, therefore, be determined 
at any fixed temperature by the composition of the liquid. 

Boiling point may be defined as "the temperature at which, under at- 
mospheric or any other specified pressure, a liquid is transformed into a 
vapor; i.e., the temperature at which the vapor pressure of the liquid equals 
the pressure of the surrounding gas or vapor" ("Hackh's Chemical Diction- 
ary/' Philadelphia, 1944). When distilling at atmospheric pressure, this 
vapor pressure corresponds to the weight of a mercury column of 760 mm. 2 
hi height. Any reduction of the pressure above a liquid causes a lowering of 
the boiling point, any increase of pressure results in a higher boiling point. 
A liquid consisting of several constituents, completely miscible in one another 
and possessing different boiling points, in most cases (except the so-called 
"constant boiling mixtures") does not have a uniform boiling point but a 
boiling range. As the lower boiling constituents vaporize or distill off, the 
boiling temperature of the liquid rises and finally approaches that of the 
highest boiling constituent. 

Next, let us consider the effect of adding to a pure liquid in equilibrium 
with its vapor a second liquid which is completely immiscible with the first 
one. This brings us to a discussion of the distillation of heterogeneous 
liquids, as in the case of essential oil distillation with steam or boiling water 
(hydrodistillation). To facilitate visualization, imagine that the two media 
are kept well stirred, so that the percentage of each liquid present remains 
the same in all parts of the mixture, including the surface. Such mixing has 
little effect on the ultimate result. Again, the rate of vaporization decreases, 
because the number of molecules of the first liquid in the surface layer is 
decreased. In this case, however, the liquids are not miscible, and the 

2 Equals 29.922 in.; or a pressure of 14.6974 Ib. per sq. in. 1.0333 kg. per sq. cm. 


vapor molecules can only be condensed when they strike a molecule of their 
own kind, so that the rate of condensation will also be decreased. Now, 
the rate of vaporization and the rate of condensation both depend upon the 
percentage of molecules of the first kind present on the surface. These 
rates will be affected equally, and there will be no change in the number of 
vapor molecules of the first component present. Applying the same reason- 
ing to the case of the other component leads to the same conclusion. We 
thus arrive at the important law that the total number of molecules present in 
the vapor space above a two-phase liquid mixture at ary gwtn temperature is 
equal to the sum of the numbers of molecules so present if either liquid were dealt 
with alone. Furthermore, since the relative amounts of the two liquids 
present have not in any way entered our reasoning, this conclusion must be 
true regardless of the relative amounts so long as both liquids are present. 
In other words, in the case of a two-phase (heterogeneous) liquid the composi- 
tion of the mixed vapor, at a given temperature, does not depend upon the com- 
position of the liquid. 

A system of water and essential oil forms a two-phase liquid; therefore, 
this type of distillation is of primary importance to the essential oil pro- 
ducer. Let us then consider further the results of the above reasoning for 
our The pressure exerted by a vapor, whether it consists of one or 
several kinds of molecules, is a manifestation of the constant bombardment 
by the rapidly moving vapor molecules hitting the walls enclosing the vapor. 
Pressure measures a force acting on a unit area, and this force, in the case of a 
vapor, results from the vapor molecules striking the wall and rebounding. 
The total pressure exerted will be equal to the pressure expended by one molecule 
multiplied by the number of molecules hitting a unit area of the wall in a unit of 
time. The kinetic energy expended by one molecule will depend on the 
temperature, but the number of collisions with the wall will depend on the 
number of molecules, of whatever kind, present in the vapor space. In 
other words, the pressure will depend on the concentration of the molecules or, 
stated differently, on the concentration of the vapor. 

Now, it has been shown that in the case of a two-phase liquid the total 
number of molecules present in the vapor phase in equilibrium with it is 
greater than the number which would be present if either pure liquid were 
present alone at the same temperature. Hence, the pressure exerted by the 
vapor mixture will be greater than that exerted by either pure vapor alone. 
In the distillation of volatile oils with steam or boiling water (hydrodistilla- 
tion), the pressure in the vapor space is maintained constant, either by con- 
necting the vapor space with the atmosphere or by suitable controls to 
maintain a reduced or elevated pressure. For definiteness we shall consider 
an operation at atmospheric pressure. If pure water is heated in a still, it 
will begin to boil (or in other words, the pressure of its vapor will equal that 


of the atmosphere), when its temperature has reached 100 C. (212 F.). 
Let us suppose that an oil insoluble in water is introduced into the still 
along with the water. If permitted to do so, the pressure in the vapor space 
would increase as previously shown. But in our case the vapor space 
is connected to the atmosphere; therefore, the pressure will be reduced to 
atmospheric pressure, which can be accomplished only by automatic lower- 
ing of the temperature. When the temperature of a liquid is lowered, the 
tendency of the liquid molecules to go into the vapor phase also decreases, 
thus decreasing the concentration of the molecules in the vapor, and conse- 
quently the vapor pressure. Hence, the temperature will be lowered to a 
value such that the total pressure exerted by the vapor mixture is again 
equal to the operating pressure (atmospheric pressure in our case). Thus 
the boiling temperature for any two-phase liquid will always be lower than the 
boiling point of either of the pure liquids at ike same total pressure. For ex- 
ample, water (boiling at 100) and benzene (boiling at 80) present two such 
insoluble liquids : when a mixture of the two is brought to a boil at atmos- 
pheric pressure (760 mm.), it vaporizes (distills) constantly at 69 so long as 
both constituents remain present in the liquid mixture. The moment either 
of the two constituents is completely vaporized (distilled off), the tempera- 
ture rises to the boiling point of the remaining constituent. Such conditions 
prevail with all volatile substances, provided they are insoluble in water or 
only very slightly soluble, and are not chemically reacted upon by water. 
When brought to boiling together with water, they vaporize at a tempera- 
ture below that of boiling water and also below those of the boiling points 
of the pure compounds insoluble in water. 

In the preceding discussion we emphasized repeatedly that the vapor in 
equilibrium with a two-phase liquid consists of two kinds of molecules. 
The total pressure exerted by such a mixture is due, therefore, to the sum of 
the pressures of each kind of molecule alone. The pressure exerted by 
either of the pure vapors at the same temperature would be the vapor pres- 
sure of that pure component, while the total vapor pressure of the mixture is 
thus equal to the sum of the partial vapor pressures. By partial pressure we 
mean the vapor pressure of any one component in a mixed vapor. Ob- 
viously for such two-phase liquid systems the partial pressure and vapor 
pressure of any component are the same. This simple rule of the additivity 
of partial pressures affords a ready means of estimating the temperature 
at which any particular steam distillation (hydrodistillation) will occur. 
The vapor pressures of the two pure components are simply tabulated at a 
series of temperatures. The operating' temperature will then be that tem- 
perature at which the sum of the two vapor pressures equals the operating 
pressure, in the above cited example the atmospheric pressure. In that 
case, the vapor pressure of water at 69 is 225 mm., the vapor pressure of 


benzene 535 mm., added together 760 mm. This condition permits the 
combined vapors of the constituents to overcome the (normal) atmospheric 
pressure; in other words, the mixture starts to boil at 69 under normal 
atmospheric pressure. In order to effect the boiling of a volatile compound 
insoluble in water, it remains immaterial whether the substance in question 
is brought to a boil with water or whether live steam is injected into the 
liquid or finely powdered substance. It is the steam (water vfcpors 
whence the term hydrodistillation) that causes the boiling (distillation, in 
our case) of the compound insoluble in water, at a 'emperature below the 
boiling point of the compound itself and below that of water. 

The composition of the vapor formed from a two-phase liquid mixture 
depends on the partial vapor pressures of the pure constituents. Thus, if 
the vapor pressure of component A is high and that of B low, the mixed 
vapor will consist very largely of component A . The ratio between the weights 
of component A and B will be given by the ratio of their vapor pressures multi- 
plied by tJie ratio of their molecular weights. As pointed out, boiling will take 
place only when the sum of the partial pressures exerted by the components 
is equal to the pressure maintained in the vapor space ; therefore, a hetero- 
geneous (two-phase) liquid boils or distills at a temperature which, at the 
same total pressure, always lies below the boiling point of the lowest boiling 
constituent, so long as the latter remains in the mixture, pt is for this 
reason primarily that hydrodistillation has been used for such a long time 
and so generally in the isolation of essential oils from aromatic plants. 
By vaporizing (boiling) mixtures of water and essential oils (also from plant 
material), the temperature will always be maintained lower than the boiling 
point of water at the same total pressure and, in this way, damage and de- 
composition of the essential oils by overheating are prevented. The fact 
that the vapor pressures of most essential oils are low relative to the vapor 
pressures of water at corresponding temperatures accounts for the fact that 
the ratio of water to essential oil in the condensate is relatively high. It 
will make no fundamental difference in the behavior of the mixture whether 
or not a steam distillation is carried out in the presence of a liquid water 
phase, but it does influence certain practical aspects of the process, as will 
be indicated in the second part of this chapter. 

In order to isolate an essential oil from an aromatic plant, the material, 
in actual practice, is packed into a still, a sufficient quantity of water added 
and brought to a boil, or live steam is injected into the plant charge. Due 
to the influence of hot water and steam, the essential oil will be freed from 
the oil glands in the plant tissue. The still, therefore, will contain a mixture 
of two liquids, viz.., hot water and volatile oil which are not mutually soluble, 
or only very slightly so. Gradually the liquid in the still is brought to a 
boil, the vapor mixture then consisting of water vapors (steam) and oil 


vapors. This vapor mixture passes through a connecting tube into a 
condenser, where it is reliquefied (condensed) by external cooling, usually 
with cold water. From the condenser the distillate flows into a receiver 
(separator), where the oil separates automatically from the distillation water. 
In the course of distillation it is necessary continuously to replace the water 
evaporating from the still, or to inject a sufficient quantity of live steam to 
vaporize all the volatile oil contained in the plant material or present in the 
still. When the last traces of volatile oil have been recovered, only pure 
water will distill over, and distillation is completed. 

As said, the composition of the distillate from a mixture of two insoluble 
liquids in other words, the weight quantities of the two substances 
depends primarily upon their boiling points, or upon their vapor pressures 
at the temperature of distillation. If, for example, we distill a water in- 
soluble compound with a boiling point of only 50, the distillate will consist 
of a certain volume of water and a larger volume of the water insoluble 
compound. If, on the other hand, a water insoluble compound with a boil- 
ing point of 300 is hydrodistilled, the distillate will contain mostly water 
and very little of the high boiling substance. Thus, in the distillation of a 
water insoluble volatile compound, the percentage of the latter in the dis- 
tillate decreases with rising boiling point of the compound. This decrease, 
however, is not uniform with all substances. Some substances with similar 
boiling points will occur in the distillate in different proportions ; others with 
a marked differential in their boiling points may accumulate in the dis 4 illate 
in almost the same proportions. Deviations of this sort are caused pri- 
marily by the chemical constitutions and reactivity of the various essential 
oil components. As explained above, the quantitative composition of the 
distillate (condensate) can be calculated in advance when hydr:xlistilling 
chemically uniform, water insoluble substances. The rule underlying hy- 
drodistillation of essential oils or volatile substances in general may be 
expressed as follows : 

The ratio between the weights of the two vapor components, and therefore of 
the two liquids in the distillate (condensate), is expressed by the ratio of their 
partial vapor pressures multiplied by the ratio of their molecular weight. 

Woll Pon Jlfoil 

in which TFn 2 o = weight of water in the condensate; 
Tfoii = weight of oil in the condensate; 
PH 2 o^ = vapor pressure of water at still temperature; 
Poll = vapor pressure of oil at still temperature ; 
Mn t o = molecular weight of water ( = 18); 

Afoii = molecular weight of oil (assuming that this constant may 
be determined as an average figure). 


Essential oils are not chemically pure substances but consist of several, 
often many, compounds possessing different chemical and physical proper- 
ties. The boiling points of the volatile oil components range in most cases 
from 150 to 300 at 760 mm. pressure. According to the preponderance of 
lower or higher boiling constituents we speak of a low boiling or of a high 
boiling oil. Distillation of an essential oil reveals its higher or lower vola- 
tility to a very marked degree if the oil is in free, direct contact with the 
boiling water or with the passing steam : in the early stages of distillation the 
lower boiling components distill over; the higher boilitg ones pass over later. 

Let us now study hydrodistillation of a volatile oil with a very simple 
example : peppermint oil is placed into a glass flask and live steam is intro- 
duced into the oil. The external pressure and temperature, in this case, 
remain immaterial, so long as at least a portion of water remains in steam 
form. The steam then causes the peppermint oil to form vapors, to vapor- 
ize, each steam bubble presenting to the vaporized oil an empty space into 
which the oil immediately sends vapor molecules. Every volume unit of 
steam will be filled with an equal volume of oil vapors, rise to the top of the 
flask and enter the condenser, where steam and oil vapors are condensed. 
The hydrodistillation of any essential oil is based upon this simple principle 
which, however, does not fully apply to the oils when they are still enclosed 
within the plant tissue. There the steam must exert yet another action of 
considerable influence, i.e., it must transmit heat. Unlike a liquid, the rigid 
plant matter is not able to conduct the heat from the still walls to all parts 
of the plant charge. The heat is actually transmitted by water, either as 
boiling water when distilling immersed plant material or as water vapors 
when distilling plants by blowing live steam into the charge. Also, the 
volatile oils occur in special oil glands, sacks or intracellular spaces of the 
plant tissue ; hence the oils must be freed, prior to distillation, by breaking 
down the plant tissue, and by opening the oil glands as much as possible, 
so that their volatile content can be readily attacked and vaporized by the 
passing steam. In unreduced, whole plant material, the oil must be freed 
during distillation by the force of hydrodiffusion, a very important feature 
which will be discussed later in more detail. 

Let us now return to the more theoretical aspects of hydrodistillation. 
In steam distillation it is frequently possible to change materially the ratio 
of water to oil in the condcnsate by changing the operating pressure. As 
pointed out earlier, this ratio is determined by the relationship 

TFlijO __ Pn t O AT HjO 

In any hydrodistillation using saturated steam, the sum of P H2 o and P u will 
equal the operating pressure and the still temperature will automatically 



adjust itself until this condition is met. As the operating pressure is low- 
ered below atmospheric pressure, the temperature of the operation will 
decrease. In general, the vapor pressure of water decreases much more 
slowly with the temperature than does the vapor pressure of an essential 
oil, so that the weight ratio of water to oil increases. Conversely, this 
ratio decreases with increasing temperature. Data for a typical case are 
given in Table 3.1. 

TABLE 3.1. 


mm. Hg 


Vapor Pressure mm. Hg 

Molal Ratio 
Water /Citronellal 





, 60 



































These data demonstrate that operation at reduced pressure results in a 
lower operating temperature, but also requires the use of more steam per 
weight unit of Citronellal recovered. Operation at elevated pressure (use 
of high-pressure steam in the still), on the other hand, permits a consid' rable 
saving in the amount of steam required per weight unit of oil, but also in- 
volves a higher operating temperature. Provided that the higher tempera- 
ture does not damage the oil, there is evidently some advantage to be gained 
by the use of high-pressure steam. Details will be discussed in the second 
part of the chapter on distillation. 

Up to this point our discussion has dealt entirely with the use of saturated 
steam. It is also possible indeed, in some cases advantageous to distill 
essential oils by using superheated steam. Pressure and temperature of 
superheated steam are no longer mutually dependent. Thus, it is feasible 
to use superheated steam at a fixed pressure and at any desired temperature 
above the boiling point at that pressure. The temperature at which such a 
distillation is carried out can thus be raised without increasing the concen- 
tration (partial pressure) of the steam. Since the temperature alone de- 
termines the vapor pressure, and consequently the partial pressure of the 
volatile oil, distillation with superheated steam results in a lower ratio of 
water to oil, accomplishing a further saving in the amount of steam used. 
In the above cited case of water and citronellal mixtures the steam would 
normally be saturated at 90. If superheated to 100 at a pressure of 526 
mm., an* then used in the distillation, the molal ratio of water to citronellal 


is reduced to 23.3 (weight ratio = 1.72), the total operating pressure then 
being 548.5 mm. By increasing the pressure of the superheated steam any 
ratio between this and 33.8 (corresponding to the use of saturated steam at 
100) can be obtained. 

Two features affecting the use of superheated steam should be pointed 
out. First, in order to obtain the above cited advantage of superheated 
steam the still must be completely free of water. When superheated steam 
comes into contact with water it immediately vaporizes some of the water, 
being itself cooled in the process and being reconverted into saturated 
steam. If the quantity of water present is small, it will be vaporized quickly 
and the process will continue as with superheated steam after the water has 
been evaporated. Second, the temperature of superheated steam is inde- 
pendent of the pressure ; hence the characteristic safeguard against overheat- 
ing common with saturated steam operation no longer remains operative. 
The temperature of the charge will reach that of the superheated steam; 
therefore, the latter temperature must be controlled carefully in order to 
avoid damage to the essential oil. Also, since there is no water present in 
the still, the plant charge tends to dry out during distillation with super- 
heated steam, and the forces of hydrodiffusion can no longer play their 
part. This causes a slowing down in the rate of recovery of essential oil, 
and in extreme cases may stop it entirely, long before the recovery is com- 
plete; in other words, the yield of essential oil will be subnormal. For all 
these reasons superheated steam distillation may be undertaken only with 

It should be mentioned in this connection that for distillation any hot 
gas (air, flue gas, etc.) could be used in place of steam but, since these gases 
are not condensable, the size of the cooler required would be so great as to 
be impracticable. 

Let us now again study the behavior of mixtures of liquids which form a 
single liquid phase. These considerations apply particularly to the frac- 
tionation of essential oils after they have been isolated from the plant ma- 
terial. As has already been pointed out, all liquids have a tendency to 
change to vapors, the extent of this tendency depending on the temperature 
at which the liquid is maintained. This tendency to vaporize may be gaged 
by the vapor pressure of the liquid. In general, the components of the 
liquid mixture will have different vapor pressures at any particular tempera- 
ture. When such a mixture is vaporized, the component with the greater 
vapor pressure (the more volatile component) consequently tends to con- 
centrate in the vapor phase, while the less volatile component will be cor- 
respondingly concentrated in the liquid phase. This condition holds for 
all mixtures of liquids which are soluble in one another, and which do not 
form constant boiling mixtures. Liquid mixtures which form 'Constant 



boiling mixtures behave somewhat differently and will not be discussed 
here. The tendency of the more volatile liquid to concentrate in the vapor 
phase can be observed very readily by reference to the accompanying 
Diagram 3.1. 

% more volatile component 


DIAGRAM 3.1. Typical boiling point and vapor-liquid equilibrium diagram for a 
single-phase binary mixture at constant pressure. 

In this diagram the composition of the liquid mixture and its boiling 
temperature have been plotted. The lower of the two curves represents the 
relationship between the boiling point of any mixture of these two compo- 
nents and its composition. The upper curve represents the composition 
of the vapor which is formed from any liquid mixture at its boiling point. 
Proceeding along a vertical line in the region below the lower curve may be 
said to correspond to heating a mixture of fixed composition without vapor- 
ization. At the temperature corresponding to the point at which this 
vertical path intersects the lower curve, this particular mixture will begin 
to vaporize, and the vapors arising first will have a composition represented 
by the intersection of a horizontal line through the boiling point of this 
mixture with the upper curve. In the particular case illustrated, a liquid 
containing A per cent of the more volatile constituent would produce an 
initial vapor containing a percentage of the more volatile constituent repre- 
sented by point B. The vapor produced is thereby enriched with the more 
volatile constituents. If the distillation is continued without adding liquid 
to the still, the liquid in the still will become progressively poorer in the 
more volatile constituents. Furthermore, on condensing and then redis- 
tilling the vapor produced, a further enrichment in the more volatile con- 
stituents will be achieved. Theoretically, then, it appears possible to ob- 
tain a vapor consisting entirely of the more volatile components by a suit- 
able number of redistillations. An effect corresponding to a series of re- 



distillations can be produced in a fractionating column such as that shown 
in Fig. 3.1. 

In this type of system the vapors rising from the still, as always partially 
enriched with the more volatile component, are essentially condensed and 
redistilled on the first section above the still. The vapors rising from this 
section are again condensed and redistilled in the next higher section, this 
process continuing to the top of the fractionation tower. Such equipment, 

Steam Inlet 


FKI. 3.1. Still with fractionating column. Schematic diagram showing essential 
parts and typical arrangement. 

then, permits obtaining a final distillate which contains a higher percentage 
of the more volatile components of the mixture than the original material 
this, too, in a single piece of equipment. Heat is supplied to such a frac- 
tionating system in the still only. On the plates in the tower above the 
still the heat liberated by condensation of the vapors furnishes in turn the 
heat necessary to revaporize the material. Of course, the entire system 
must be insulated thoroughly in order to prevent excessive condensation 


of vapors due to the heat losses from the tower. In actual operation, such a 
tower would ordinarily be run by returning part of the condensate at the 
top to the top plate as reflux. The greater the ratio of reflux to product, 
the more complete will be the separation of the more volatile from the less 
volatile components. A system of this kind can be operated at any desired 
pressure either above or below normal atmospheric pressure. In the final 
purification of many essential oils (not hydrodistillation), the operation must 
proceed at very low pressures in order to avoid overheating and consequent 
destruction of the material. The number of plates required in the frac- 
tionation tower is determined largely by two factors : 

1. The relative volatility of the components of the mixture. 

2. The extent of separation required or desired. 

Whenever one component is much more volatile than the other, only a 
few plates will be necessary to give a high degree of separation, but when the 
volatilities are more nearly equal, the number of plates must be greatly 
increased. A rough estimate of the relative volatilities can be drawn from 
the boiling points at atmospheric pressure of the components of the mixture. 
There exist quite satisfactory methods for calculating the number of plates 
required for any particular separation. Details of these methods go beyond 
the scope of this work and those interested should consult references. 3>4t5 

The above considerations show that sorne separation of the components 
of a mixture of mutually soluble constituents (such as essential oils) can be 
achieved simply by vaporizing the mixture and condensing the vapors. 
Usually, however, this separation will be relatively small, and it will be 
necessary to resort either to redistillation of the condensate or to the use of 
fractionating towers as indicated. 

In order to consider in more detail the behavior of mixtures of soluble 
liquids, let us take the case of a mixture of only two constituents. The same 
principles apply to more complex mixtures, but will be easier to follow in 
the simpler case. In single-phase mixtures the tendency of either com- 
ponent to vaporize will depend on the temperature of the mixture, and on 
its composition. In the simplest case, the partial pressure of one consti- 
tuent will be given by the expression 

pi = Pi X Ni (1) 

8 Robinson and Gilleland, "Elements of Fractional Distillation," McGraw-Hill, New 
York, 1939. 

4 Badger and McCabe, "Elements of Chemical Engineering," McGraw-Hill, New York, 

5 Walker, Lewis, Me Adams and Gilleland, "Principles of Chemical Engineering," 
McGraw-Hill, New York, 1937. 



in which p\ 

= partial pressure of constituent 1 ; 

= vapor pressure of pure constituent 1 at the temperature of 

the liquid; 
= mol fraction of constituent 1. 



Mi M 2 

Wi weight of constituent 1 in mixture; 
Wz weight of constituent 2 in mixture ; 
MI = molecular weight of constituent 1 ; 
M 2 = molecular weight of constituent 2. 

The relationship between the partial pressures of the constituents, total 
pressure of the mixture (which is equal to the sum of the partial pressures) 
and the composition of the mixture for a fixed temperature is shown in 
Diagram 3.2. Systems which follow this rule are ideal systems and are 
said to obey Raoult's law (Equation (1) above). 

Mol fraction more volatile component 

DIAGRAM 3.2. Partial and total pressure curves at constant temperatures for a 
single-phase binary mixture obeying Raoult's law. 

In the more general case, the relationships between these variables are 
not as simple and can be determined only by experimental methods. A 
typical case is shown in Diagram 3.3. 

Since most distillations are conducted at constant pressure rather than 
at constant temperature, and since the boiling point of a mixture at a 
fixed pressure varies with the composition, a somewhat more useful diagram 
for purposes of analyzing distillation problems is shown in Diagram 3.4. 

This diagram represents the composition of the vapor corresponding to 
the composition of the equilibrium liquid mixture at a constant total pres- 



Mol fraction more volatile component 1.0 

DIAGRAM 3.3. Partial and total pressure curves at constant temperature for a 
single-phase binary mixture showing one type of deviation from Raoult's law. 

sure. Both compositions are expressed in terms of the percentage of the 
more volatile constituent, and obviously the vapor is always richer in this 

component than is the liquid from 
which it originated. Thus, the 
vapor in equilibrium with a liquid 
of composition A would have the 
composition B. If this vapor were 
entirely condensed, the resulting 
liquid would have this same com- 
position B and, if redistilled, would 
give an equilibrium vapor, further 
enriched and having composition C. 
This is essentially the process which 
takes place in a f ractionation column. 
The mechanism which accomplishes 
separation in this type of equipment 
is evident. The effects of changing 

Mol fraction in liquid 

DIAGRAM 3.4. Vapor-liquid equilibrium 
diagram at constant temperature for a 
single-phase binary mixture. (All composi- 
tions expressed in terms of the more volatile 

reflux ratio and other variables can- 
not be discussed here in detail. 

Although a fractionating tower 
consisting of separate plates as shown 
in Fig. 3.1 has been used as an example, an equally satisfactory tower for most 
purposes consists of an open column filled with a suitable packing material. 
This material can take almost any conceivable shape, but should be charac- 



terized by low density (weight per unit volume of the packing), relatively 
large amount of open space and a large surface area. For example, crushed 
rock can be used as packing, but because of its high density and low per- 
centage of open space would not be very efficient. Several typical packing 
materials are shown in Fig. 3.2. 

Courtesy U. S. Stoneware Co., Akron, Ohio. 

FIG. 3.2. Raschig rings. 

In the distillation of single-phase mixtures, it should be kept in mind 
that changing the pressure in the still has only a minor effect on the overall 
operation. Since in the distillation of essential oils the principal reason for 
ever operating at pressures other than atmospheric is to lower the distillation 
temperature, the pressure will usually vary between atmospheric and some 
lower pressure, thus limiting the possible variations in pressure. The 
efficiency of any particular piece of equipment may be changed slightly by 
operating at different pressures, but the net result will be practically un- 
affected. This holds true particularly in the case of mixtures such as those 
encountered in the purification and fractionation of essential oils. 



Lb. per Sq. In. 

Kg. per Sq. Cm. 

Mm. of Mercury 















































































Having indicated briefly the general principles of distillation of homo- 
geneous and heterogeneous systems, we shall devote the second part of this 
chapter to a discussion of the practical distillation problems and techniques 
peculiar to the essential oil industry. 

(a) Treatment of the Plant Material. 

Comminution of the Plant Material. The chief application of distillation 
is in the initial isolation of essential oils from the aromatic plant material. 
This process involves the handling of predominantly solid products, and 
the preparation of the material must, therefore, be carried through carefully 
if the most efficient and complete recovery of the valuable essential oils is 
to be assured. The essential oils are enclosed in "oil glands," "veins/* 
"oil sacks," or "glandular hairs" of the aromatic plants. If the plant ma- 
terial were left intact, the oils could be removed (vaporized) by the steam 
only after they had passed through the plant tissues to an exposed surface. 
This can be accomplished only by hydrodiffusion, a mechanism which will 
later be shown to play a very important part in plant distillation. Diffu- 
sion is always a slow process, and if the plants or parts of plants were left 
intact, the rate of recovery of oil would be determined entirely by the rate of 
diffusion. Consequently, before distillation, the plant material must be 
disintegrated to some extent. This disintegration process, commonly 
termed comminution, results in exposing directly as many oil glands as is 



practically possible. It always reduces the thickness of material through 
which diffusion must occur, greatly increasing the rate or speed of vaporiza- 
tion and distillation of the essential oils. Even in comminuted plant ma- 
terial, only a portion of the oil is freed, the balance remaining enclosed or 

Courte*)/ of Sprout, Waldron & Co., Muncy, Pa. 

FIG. 3.3. 3-Pair high roller mill. 

being tightly covered by comminuted plant particles. All actually exposed 
volatile oil will soon be entrained by passing steam and carried away from 
the plants. 

The extent of comminution required varies with the nature of the plant 
material. Flowers, leaves and other thin and nonfibrous parts of the plant 


can be distilled without comminution. The cell walls in these parts are in 
most cases sufficiently thin and permeable to permit rapid removal of the oil. 
Seeds (fruits), on the other hand, must be thoroughly crushed in order to 
rupture as many of the cell walls as possible, to render the oil easily accessible 
to the passing steam. Roots, stalks and all woody material should be cut 
into short lengths in order to expose a great number of oil glands. 

Seeds can best be crushed by passing them through smooth rolls. These 
rolls should be arranged so that the distance between them can be varied. 
The width of this space will determine the extent of crushing obtained. A 
similar effect can be achieved by regulating the flow of the material upon the 
distributor above the rolls. If the rolls operate at different speeds, the crush- 
ing action is supplemented by a usually advantageous shearing action. 
Each roll should also be equipped with a scraping device, called a "doctor 
blade," which serves to keep it free of adhering crushed material. A typical 
piece of equipment for handling seeds and fruit is shown in Fig. 3.3. 

Roots and stalks can best be handled in a hay or ensilage cutter, or 
similar device. This action simply reduces the long natural parts of the 
plant to short lengths which are more readily handled in the distillation 
proper and, above all, assures a more uniform and compact charge in the 
still. Otherwise the live steam would find ready passages through the wide 
interspaces of uncut roots or stalk material and escape without coming in 
close contact with all plant particles. The result, especially in the case of 
steam distillation, would be a very inferior yield of oil. Woody parts may 
be sawed into small pieces or chipped mechanically. Typical machines for 
handling these raw materials are shown in Fig. 3.4. 

The principal purpose of comminution being to render the essential 
oils more readily removable by the passing steam, it is evident that once the 
plant material has been crushed or reduced in size it must be distilled im- 
mediately. Otherwise, the essential oils, being somewhat volatile, will 
partly evaporate, with two adverse effects: first, the total yield of oil will 
be reduced by an amount equal to the extent to which evaporation has 
occurred ; second, the composition of the oil will change, thereby affecting 
its odor. This second effect results from the fact that the essential oils 
are mixtures of several, often numerous, compounds, the more volatile 
components evaporating to a greater extent than the higher boiling and less 
volatile ones. In the case of crushed caraway seed, for example, the evapo- 
ration loss consists mainly of limonene, which is lower boiling than carvone ; 
the oil distilled from crushed seed which has been left in contact with open 
air for some time will, therefore, possess also a somewhat higher specific 
gravity. The extent of these oil losses by evaporation can be demonstrated 
easily by crushing a small quantity of caraway seed, weighing it on an an- 
alytical balance, airing it for a few minutes and checking the weight. Von 



Rechenberg 6 reported a loss of 0.5 per cent which he attributed entirely to 
evaporation of oil, not of moisture, because air-dried seed was used in the 
experiment. It is, therefore, imperative that comminution be carried out 


Courtesy the W. J, Fitzpatrick Co., Chicago, III. 

FiQ. 3.4. Stainless, non-corrosive comminuting machine. 

immediately before the product is charged into the still if highest yields and 
best quality oils are to be obtained. 

After the plant materials have been properly prepared for distillation, 
they are packed into the still and distillation can be started. Methods of 

6 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig (1910), 391. 


charging and the construction of the still itself will be discussed after the 
general distillation methods have been presented. 

Storage of the Plant Material. The storage of plant material before com- 
minution also offers some hazard in the way of ultimate loss of volatile oil. 
The situation here is not quite so serious as in the case of comminuted ma- 
terial and, therefore, if a delay in the distilling of the plant material cannot 
be avoided, it should be stored in its natural condition. Gradual evapora- 
tion results in some loss under these circumstances, the major sources of 
loss being represented by oxidation and resinification of the essential oils. 
If the plant material must be stored before processing, it should be kept in a 
dry atmosphere at a low temperature, and in a room free from air circula- 
tion if possible in an air-conditioned storehouse. All such losses are 
obviously avoided if the plants are processed immediately. 

Loss of Essential Oil in the Plant Material Prior to Distillation. The 
volatile oil enclosed in the plant tissue is usually in one way or another 
affected by the drying of the plant material after the harvest. This effect 
has been studied and described by von Rechenberg 7 whose findings are so 
interesting that the author feels justified in quoting a few passages of that 
work almost verbatim. 

Some fresh plants, or parts, with a high water content (e.g., roses, tansy, 
calamus root) lose much of their essential oil by air drying; others very little. 
This loss is caused by evaporation, oxidation, resinification and other chem- 
ical actions. Contrary to expectation, evaporation here seems to play a 
subordinate role to oxidation and resinification. Indeed, actual evaporation 
of the volatile oil through the walls of the plant tissue cannot take place 
readily because the oil must first be brought to the surface through hydro- 
diffusion, with water or plant moisture acting as a carrying medium. Thin- 
walled flowers and leaves present no obstacle to the forces of diffusion, and 
in most cases evaporation will affect the more water-soluble constituents of a 
volatile oil rather than the low boiling terpenes. Arriilaga, Colon, Rivera 
and Jones 8 showed that by field drying and stacking of citronclla grass or 
lemongrass prior to distillation the total acetylizable constituents of the 
oil decreased considerably with time after cutting. Since losses of acetyl- 
izable constituents were sufficient to account for most of the decrease in 
yield of oil, these authors concluded that the major factor leading to a loss 
of oil was oxidation. Evaporation of whole oil accounted for the additional 
loss. With both grasses it can be concluded that, for the best results, field 
drying, with or without subsequent stacking, should not be practiced. 

According to von Rechenberg, distillation experiments seldom give 
reliable data on the loss of volatile oil by evaporation during plant drying. 

7 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig (1910), 279. 

8 Am. Perfumer 46 (May 1944), 49. 


The reason is simply that distillation of plant material with a high water 
content usually leaves doubt as to its completeness. Peppermint offers a 
classical example in this respect. Formerly it was assumed that its oil 
content increases during the drying of the cut herb, but systematic distilla- 
tion experiments proved the fallacy of this assumption. Fresh peppermint 
herb, like most plants or plant parts with a high moisture content, simply 
cannot be exhausted completely by distillation, or only with great difficulty, 
and after long hours of distillation. By distilling one portion of peppeimint 
herb in the fresh state right after the harvest, and the other portion in 
wilted, almost dry ("clover dry") condition, and by calculating the yields 
upon 100 kg. of fresh herb, it has been shown that the fresh herb contains a 
little more, possibly much more, oil than the dried herb, but it is very diffi- 
cult to exhaust the fresh herb completely by distillation. 

The loss of oil during the period of wilting and drying of the plant ma- 
terial is much greater than the loss occurring during storage of the plant 
material after it has been dried. This may be explained by the fact that, 
during the first stages of wilting and drying, the plant retains a large amount 
of moisture in the cells, which by diffusion carries the oil to the surface, and 
aids in its vaporization. Once the moisture has disappeared, and the plant 
has become air dried, hydrodiffusion can no longer take place. Any loss of 
oil during storage of the air dried plant material depends upon several fac- 
tors condition of the material, method and length of storing, and the 
chemical composition of the oil. As a rule, but with many exceptions, 
flowers, leaves and herbs do not endure prolonged storing, whereas seeds, 
bark, roots and wood, by their very nature, retain their volatile oils much 
longer. Method of storing (packing tightly in sacks or bales, or spreading 
on the floor and heaping loosely) plays an important role in this respect. 
Air currents and extreme variations in moisture content of the atmosphere 
favor oil evaporation, resinification and, particularly, oxidation. It is 
possible to keep many types of plant materials for a long period, provided 
they are stored at sufficiently low temperature and in an air-conditioned 
room. Under such conditions, caraway seed docs not lose volatile oil even 
over a period of six months. In isolated cases, plant materials guaiac wood 
and sandalwood, for example retain their essential oil for many years, even 
though exposed to considerable variations of weather. 

Von Rechenberg claims that the greatest loss of volatile oil by evapora- 
tion and oxidation occurs in comminuting the plant material prior to dis- 
tillation, especially if this is done in rapidly rotating grinders and mills. 
The extent of loss depends upon the speed of air circulation in the system, 
the degree of heat development in the material, and the composition of the 
volatile oil (its boiling range and resistance to oxidation). 


Change in the Physicochemical Properties of Essential Oils During Plant 
Drying. Essential oils distilled either from fresh or from dried plant parts 
show wide variations in physicochemical properties and chemical composi- 
tion. With many oils it seems advisable, therefore, to state whether they 
were distilled from fresh, wilted, or air-dried plant material. This is es- 
pecially true of flowers, leaves, herbs and roots, which in the fresh state 
contain much moisture. 

Peppermint oil, for example, displays marked variations in its properties. 
Oil from fresh herb, according to von Rechenberg, 9 had a specific gravity of 
0.908, that from clover dried herb a gravity of 0.912. (The term "clover 
dried" means that the stalks are still flexible but the leaves dry.) 

A series of interesting distillation experiments were carried out by 
Schimmel & Company : 1() 

Angelica Root Oil 

From fresh angelica roots: d\l 0.857 to 0.860 
From dried angelica roots: d\l 0.870 to 0.902 

The specific gravity of angelica root oil increases in proportion to the 
length of time the roots have been stored. 

Lovage Root Oil 

From fresh lovage roots: d;* 1.002 to 1.035 
From dried lovage roots: d\* 1.039 to 1.040 

Fresh and dried lovage roots exhibit a difference in behavior during dis- 
tillation. During the distillation of dried lovage root, a yellow, gluey, 
resinous mass appears together with the oil, especially toward the end of 
distillation. This mass is largely dissolved in the oil ; part of it separates in 
the condenser pipes, and in the Florentine flask. Fresh lovage roots do not 
yield this resin, and wilted roots in only a small amount. Oil of lovage from 
fresh roots, when rectified, is entirely volatile ; the oil from dried roots upon 
rectification leaves in the still considerable quantities of a high boiling resi- 
due, which cannot be redistilled with water or steam. 

Calamus Root Oil 

From fresh calamus roots: dj* 0.962 to 0.968; D +20 to +31 
From dried calamus roots: d\l 0.903 to 0.978; D +15 to 4-20 

The oil from the fresh roots is more soluble in 70 per cent alcohol than 
is the oil from the dried roots. The solubility of the oil decreases with 
aging (storing) of the root. 

9 "Theorie dcr Gewimumg und Trennung dcr atherischen Clc," Leipzig (1910), 270. 

10 Ber. Schimmel & Co., April (1895), 9. 


Estragon Oil 

From fresh estragon herb: d\l 0.918 to 0.934; D +2 to +4 
From dried estragon herb: d\l 0.890 to 0.923; D +5 to +8 

Tschirch 11 reported interesting observations on the resinifioation of 
volatile oils in spice plants. Whether the formation of these so-called resins 
is caused by the polymerization of homogeneous compounds or the addition 
reactions of heterogeneous compounds, by oxidation, or other forms cf con- 
version of volatile compounds, is not entirely clear. 

Natural (not rectified) peppermint oil distilled fro* a fresii herb is more 
soluble in 70 per cent alcohol than is the oil distilled from dried herb, but 
the solubility decreases after a few months. If oil from fresh herb is rec- 
tified, it resinifies again, whereas oil from dried herb, when rectified, retains 
its original solubility. Certain constituents of peppermint oil, including 
possibly menthofurane, seem to resinify during the drying of the herb. 

During wilting and drying, the cell membranes gradually break down, 
and the liquids are free to penetrate from cell to cell, giving rise to the forma- 
tion of new volatile compounds e.g., by glycoside splitting. A typical 
example is found in bitter almond oil, which develops in the course of brief 
storing of crushed and moistened almond or apricot kernels. In the live 
fruit, the enzyme (emulsin) cannot contact the glucoside (amygdalin) in 
aqueous solution ; but it can readily do so in the crushed and wetted kernels. 
Analogous reactions and cleavages undoubtedly take place in many other 
cases. Fresh orris roots, for example, possess a rather disagreeable "green" 
and "herby" odor; whereas the dried roots, upon aging, develop a faint 
violet odor. Freshly harvested patchouli leaves are almost odorless; the 
well-known typical patchouli odor develops only on drying and curing. 
Vanilla beans constitute another example, the fresh pods resembling to some 
degree our common garden beans. The odor of grass is very different from 
that of hay, which develops its typical coumarin note only during the drying 
process. A phenomenon not yet explained is the disappearance of geraniol 
in dried roses, while the content of phenylethyl alcohol seems to increase. 

(b) General Methods of Distillation. No investigation has yet been 
undertaken of the process by which steam actually isolates the essential oil 
from aromatic plants. It is commonly assumed that the steam penetrates 
the plant tissue and vaporizes all volatile substances. If this were true, 
the isolation of oil from plants by hydrodistillation would appear to be a 
rather simple process, merely requiring a sufficient quantity of steam. 
However, such is not the case. In fact, hydrodistillation of plants involves 
several physicochemical processes which will be discussed later. 

11 "Harze und Harzbehalter," 2nd Ed. (1906), Vols. I and II. 



There has developed in the essential oil industry a terminology which 
distinguishes three types of hydrodistillation. These are referred to re- 
spectively as : 

1. Water distillation ; 

2. Water and steam distillation ; 

3. Direct steam distillation. 

Originally introduced by von Rechenberg, the above terms have be- 
come established in the essential oil industry and will, therefore, be retained 
in our discussion. In order to avoid needless repetition, their significance 
will be indicated at this point. All three methods are subject to the same 

Courtesy of Fritzsche Brothers, Inc., New York. 

PLATE 1. A typical old-fashioned lavender still as used years ago by the lavender oi 
producers in Southern France. Only a few of these stills are being employed today. It is 
a typical water distillation, the still being heated by a fire beneath. 

general theoretical considerations presented in the first part of this chapter 
which dealt with distillation of two-phase systems. The differences lie 
mainly in the method of handling the plant material. 

Water Distillation. When this method is employed, the material to be 
distilled comes in direct contact with boiling water. It may float on the 
water or be completely immersed, depending upon its specific gravity and 
the quantity of material handled per charge. The water is boiled by ap- 
plication of heat by any of the usual methods i.e., direct fire, steam jacket 
closed steam coil, or, in a few cases, open or perforated steam coil. The 



characteristic feature of this method lies in the direct contact it affords be- 
tween boiling water and plant material. Some plant materials (e.g., 
powdered almonds, rose petals, and orange blossoms) must be distilled while 
fully immersed and moving freely in boiling water, because on distillation 
with injected live steam (direct steam distillation) these materials agglu- 
tinate and form large compact lumps, through which the steam cannot 

Water and Steam Distillation. When this second common method of 
distillation is used, the plant material is supported on a perforated grid 
or screen inserted some distance above the bottom of f he stiil. The lower 

CourfMV of Fritttche Brothers, Inc., New YorK. 

PLATE 2. A field distillery of lavender in Southern France. A typical case of water 
and steam distillation. Many of these stills are in use today in the lavender regions of 
Southern France. For discharging of the spent plant material the stills can be tilted. 

part of the still is filled with water, to a level somewhat below this grid. 
The water may be heated by any of the methods previously mentioned. 
Saturated, in this case, wet, steam of low pressure rises through the plant 
material. The typical features of this method are : first, that the steam is 
always fully saturated, wet and never superheated ; second, that the plant 
material is in contact with steam only, and not with boiling water. 

Steam Distillation. The third method, known as steam distillation or 
direct steam distillation, resembles the preceding one except that no water is 
kept in the bottom of the still. Live steam, saturated or superheated, and 



frequently at pressures higher than atmospheric, is introduced through open 
or perforated steam coils below the charge, and proceeds upward through 
the charge above the supporting grid. 

In so far as the distillation process itself is concerned, and from the 
purely theoretical point of view, there should be no fundamental difference 
between these three methods. There exist, however, certain variations in 
practice, and in the practical results obtained, which in some cases are con- 
siderable; they depend on the method employed, because of certain reac- 
tions which occur during distillation. 

Courtesy of Fritzsche Brothers, Inc., Netu York. 

PLATE 3. Field distillation of lavender flowers in Southern France. The steam is generated 

in a separate steam boiler. 

The principal effects accompanying hydrodistillation are : 

1. Diffusion of essential oils and hot water through the plant membranes, 
whence the term hydrodiffusion ; 

2. Hydrolysis of certain components of the essential oils ; 

3. Decomposition occasioned by heat. 

These effects will be considered in order. 

The Effects of Hydrodiffusion in Plant Distillation. Even after the plant 
material has been carefully prepared by proper comminution, only part of 
the essential oil is present on the surfaces of the material and immediately 
available for vaporization by steam. The remainder of the oil arrives at 
the surface only after diffusing through at least a thin layer of plant tissue. 


The term diffusion, as used in this connection, implies the mutual penetra- 
tion of different substances until an equilibrium is established within the 
system. Such diffusion is caused by the live force of molecules. Where 
two substances are not separated by a wall (diaphragm), the term u free 
diffusion" is applied, whereas diffusion through a permeable rn< -mbrane is 
called osmosis. The diaphragm may be permeable by only one sui stance, 
or by all. 

The distillation of plant material is connected with processes of di (fusion, 
and principally of osmosis. In the steam distillation of plant material 
the steam does not actually penetrate the dry cell membranes. This can 
easily be proved by distilling plants with superheated (dry) steam. The 
plant charge, in this case, finally dries out completely, and yields the retained 
volatile oil only when saturated (moist) steam is applied, after superheated 
(dry) steam no longer vaporizes the oil. Thus, dry plant material can be 
exhausted with dry steam only when all of the volatile oil has first been 
freed from the oil bearing cells by previous very thorough comminution of 
the plants. 

Entirely different conditions obtain if the plant tissue is soaked with 
water. The exchange of vapors within the tissue of living plants is based 
primarily upon their permeability while in swollen condition. Microscopic 
studies have led some to believe that the walls of normal plant cells are 
almost impermeable for volatile oils. According to von Rechenberg, only 
limited osmosis of volatile oil can take place at ordinary temperatures. This 
may easily be proved by soaking uncomminuted dried spices (such as cinna- 
mon or cloves) in cold water for a day or two, then pouring off and distilling 
the water. The yield of oil, if any, will be negligible, all the oil being retained 
within the plant tissue. If, on the other hand, the spices (or other plant 
material) are first sufficiently powdered so that the cell walls are broken 
and the oil liberated, the water poured off contains considerable quantities 
of essential oil. 

Distillation offers better conditions for the osmosis of oil, because 
the higher temperature and the movement of water, caused by temperature 
and pressure fluctuations within the still, accelerate the forces of diffusion 
to such a point that all the volatile oil contained within the plant tissue 
can be collected. The effect of a higher temperature may easily be demon- 
strated by repeating the above described experiments, but by soaking the 
spices in hot, instead of cold water. The hot water will extract much larger 
quantities of oil. 

Von Rechenberg describes the process of hydrodiffusion, in the case of 
plant distillation, as follows : At the temperature of boiling water a part of 
the volatile oil dissolves in the water present within the glands. This oil- 
in-water solution permeates, by osmosis, through" the swollen membranes, 


and finally reaches the outer surface, where the oil is vaporized by passing 
steam. Replacing this vaporized oil, additional quantities of oil go into 
solution and, as such, permeate the cell membranes while water enters. 
This process continues until all volatile substances are diffused from the 
oil glands and are vaporized by the passing steam. 

The speed of oil vaporization in hydrodistillation of plant material is 
influenced not so much by the volatility of the oil components (or in other 
words by the differential in their boiling points), as by their degree of solu- 
bility in water. If von Rechenberg's assumption is correct, the higher 
boiling, but more water-soluble, constituents of an oil enclosed within the 
plant tissue should distill before the lower boiling, but less water-soluble, 
constituents. That this actually takes place can be demonstrated by steam 
distilling comminuted and uncomminuted caraway seed. Uncomminuted 
(whole) caraway seed will first yield the higher boiling, but more water- 
soluble, carvone and only later the lower boiling, but less water-soluble, 
limonene. With crushed seed the opposite is true: the first fraction con- 
sists of limonene, the following of carvone. The fact that occasionally the 
final fraction may contain some limonene only goes to show that, as a result 
of incomplete comminution, the forces of hydrodiffusion come into play 
anew. Distillation of uncrushed caraway seed requires almost twice as 
much time as that of crushed. This well-known fact applies to distilla- 
tion of all seed material. The explanation is simply that hydrodiffusion 
acts only slowly, and requires time: in the distillation of uncrushed seeds, 
all volatile oil enclosed within the plant tissue must first be brought to the 
surface of the seeds by hydrodiffusion. 

It is a well known fact, borne out by experience, that comminution 
(crushing) of seed material increases the yield of oil. This, however, does 
not imply that uncomminuted plant material always gives a veiy low oil 
yield. Von Rechenberg 12 soaked whole (uncrushed) caraway seed in tepid 
water until it became swollen, and distilled it with direct, saturated steam 
at pressure of 5 atmospheres in a well-insulated still. He thus obtained a 
very slightly lower yield of oil than by distilling crushed caraway seed. 
This small loss consisted exclusively of carvone, which had been resinified 
during the longer hours of distillation required for uncrushed, thoroughly 
wetted seed. Such soaking, steeping, or macerating of plant material was 
frequently resorted to in the old days of small-scale distillation, when satu- 
rated steam of high pressure, generated in a separate steam boiler, was not 
yet available. In fact, steeping in water as a preliminary process should 
not be condemned in the case of seed material containing relatively low 
boiling volatile oils caraway, fennel, coriander seed, for example. Ob- 

12 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig (1910), 430. 


viously this process requires more steam, fuel, time and equipment, but the 
oil yield will be about normal, provided distillation has been carefully car- 
ried through. It should be borne in mind, however, that saturated steam 
of low pressure, if not properly employed, may easily result in a thorough 
wetting of the plant charge, and that this factor becomes much more trouble- 
some with a comminuted charge than with an uncomminuted '>ne. Von 
Rechenberg performed experiments in point with dill, ajowan and fennel 
seed, as well as with cloves and clove stems. His results again prove that, 
in the case of uncomminuted material, the oil constituents vaporize .tecord- 
ing to the degree of their solubility in water, and not iu the sequence of their 
boiling points: carvone distills before limonene in the case of dill seed; 
thymol before pinene, dipentene and p-cymene in the case of ajowan seed; 
anethole before fenchone in the case of fennel seed; methyl amyl ketone 
before eugenol and caryophyllcne in the case of cloves ; eugenol before cary- 
ophyllene in the case of clove stems. In von Rechenberg's experiments the 
distillation of uncomminuted material required twice as many hours as 
that of comminuted material, and the yield of oil was slightly, and in some 
cases considerably, lower. 

The presence of some water is distinctly beneficial in that it increases 
the rate of removal of essential oils by distillation, and it would appear, 
from this fact alone, that water distillation or water and steam distillation 
should be preferred to steam distillation. However, the maximum tem- 
perature that can be obtained with water distillation, and water and steam 
distillation, is limited entirely by the operating pressure in the still, which in 
ordinary operation equals atmospheric pressure. A complete summary 
of the advantages and disadvantages of the three methods of distillation 
will be given after the other factors affecting distillation have been discussed. 
It should be remembered, too, that all essential oils are soluble in hot water 
to at least a slight degree; therefore, the amount of water present will de- 
termine the extent to which the yield of oil will be decreased as a result of 
the retention (by water in the still) of oil, or certain constituents of the oil. 
This factor is of special importance in water distillation, since all of the es- 
sential oil must first go through the water solution stage, and the water 
in the still will always be very nearly saturated with oil, especially with the 
more water-soluble constituents of an oil with phenylethyl alcohol for 
example, in the case of rose distillation. The situation is not quite so serious 
in the case of water and steam distillation because a little of the oil dissolves 
in the still water only as a result of drainage from the still charge which is 
mechanically separated from the still water. The extent of this drainage 
will depend upon the amount of condensation taking place within the plant 
charge, and especially along the still walls, but it can be kept at a minimum 
by suitable insulation of the still. 


The Effect of Hydrolysis in Plant Distillation. The second effect accom- 
panying distillation of plant material is hydrolysis. Hydrolysis in our case 
can be defined as a chemical reaction between water and certain consti- 
tuents of the essential oils. These natural products consist partly, and in 
some instances largely, of esters, which are compounds of organic acids and 
alcohols. In the presence of water, and particularly at elevated tempera- 
tures, the esters tend to react with the water to form the parent acids and 
alcohols. Two characteristic features are important in determining the 
effect of these reactions during distillation. In the first place, the reactions 
are not complete in either direction. Starting with the ester and hot water, 
only a part of the ester will react, so that when equilibrium is reached there 
will be present in the system esters, water, alcohols and acids. Similarly, 
if only alcohols and acids had been present at the start, all four constituents 
would be present when equilibrium is established. The relationship be- 
tween the concentrations of the various constituents at equilibrium may be 
written as 

X ( a l con l) X (acid) 
~~ (ester) X (water) 

in which K = a constant value at any fixed temperature ; 

(alcohol) = molal concentration of alcohol at equilibrium; 
(acid) = molai concentration of acid at equilibrium; 
(ester) = molal concentration of ester at equilibrium; 
(water) = molal concentration of water at equilibrium. 

Consequently, if the amount of water, and hence its concentration, is 
large, the amounts of alcohol and acid will also be large and hydrolysis will 
proceed to a considerable extent. As a result, the yield of essential oil will 
be correspondingly decreased. This result is one of the principle dis- 
advantages of water distillation, since the amount of water present is always 
large, and hydrolysis relatively extensive. In the case of water and steam 
distillation, the degree of hydrolysis is much less ; it is even less with steam 
distillation, particularly with slightly superheated (dry) steam. 

As second important characteristic of hydrolysis reactions in the dis- 
dillation of essential oils, it should be noted that hydrolysis proceeds at a 
measurable rate. The fact that these reactions are not infinitely rapid 
means that the extent to which they proceed will depend upon the time of 
contact between oil and water ; this holds particularly true for short periods 
of contact. This is another obvious disadvantage of water distillation, 
since the oil and water have a maximum time of contact under the condi- 
tions there employed. 

The Effect of Heat in Plant Distillation. The third important effect ac- 
companying distillation is the influence of temperature on essential oils. 


The pressure of distillation (atmospheric, excess or reduced) can be selected 
at will, but the temperature of the steam/vapor mixture rising through the 
charge in the still varies and fluctuates in the course of the operation. It 
is lowest at the beginning because the lowest boiling constituents of the 
volatile substances, freed by comminution of the plant material, vaporize 
first. As the higher boiling constituents begin to predominate in tae vapors, 
and as the quantity of oil vapors per se in the steam/ vapor mixture decreases, 
the temperature gradually rises, until it reaches that of saturated stos ,m at 
the given pressure. Practically all constituents of e^sentia 1 oils are some- 
what unstable at high temperatures. In order to obtain the best quality 
of oil, it is therefore necessary to insure that during distillation the essential 
oils (or the plant material) are maintained at low temperature or, at worst, 
that they be kept at a high temperature for as short a time as possible. 
So far as operating temperature is concerned, there is really little choice 
between the three commonly used methods of distillation. In the case of 
water distillation, or water and steam distillation, the temperature is de- 
termined entirely by the operating pressure. If the still is open to the 
atmosphere the usual procedure the temperature will be at, or slightly 
below, 100 C (212 F.). If a valve is inserted between the still and con- 
denser, and if the apparatus is sufficiently strong to withstand the pressure, 
the still can be operated at pressures above atmospheric, and at tempera- 
tures correspondingly above 100. In the case of steam distillation, the 
operating temperature will be at, slightly below, or above 100, even at 
atmospheric pressure, depending on whether low pressure saturated or 
superheated steam is used. Any of the methods may be operated at tem- 
peratures below 100 by use of suitable pressures below atmospheric. 

Conclusions. Although the three processes of diffusion, hydrolysis and 
thermal decomposition have been considered independently, it must be 
remembered that in practice all three occur simultaneously, and hence they 
will frequently affect one another. This holds particularly true of the 
effect of temperature. The rate of diffusion usually will be increased by 
higher temperatures. The solubility of the essential oils in water an 
important factor, as indicated above in most cases also increases with 
higher temperatures. The same holds true of both the rate and extent of 
hydrolysis. Since the products of hydrolysis are in general more water 
soluble, they will also affect the diffusion process. Hence, a complete 
analysis of the various processes incidental to distillation offers a difficult 
problem. In general, observance of the following principles leads to the 
best yields, and to a high quality of essential oil : (1) maintenance of as low a 
temperature as is feasible, not forgetting, however, that the rate of produc- 
tion will be determined by the temperature ; (2) in the case of steam distil- 
lation, use of as little water as possible in direct contact with plant material, 


but keeping in mind that some water should be present in order to promote 
diffusion; (3) thorough comminution of plant material before distillation, 
and very careful, uniform packing of the still charge, remembering, however, 
that in all but water distillation excessive comminution will result in chan- 
neling of steam through the mass of plant material, thus reducing efficiency 
because of poor contact between steam and charge. 

A brief resume* of the advantages and disadvantages of the three distilla- 
tion methods in the light of the above discussion will be helpful, and is 
presented below. 

For small-scale installations, particularly in portable units, water dis- 
tillation or water and steam distillation offers the advantage of simplicity 
of equipment. The latter method is rapidly superseding water distillation 
(except in a few special cases) because of the better quality and yield of oil, 
and higher rate of vaporization, i.e., speedier distillation. 

For larger and fixed installations, steam distillation unquestionably 
offers the most advantages. In such plants the necessary control can be 
readily installed, and under these conditions the quality, yield and rate of 
oil aro superior. Also, as a result of possibility of temperature control, the 
method is more adaptable. Plant materials containing either low or high 
boiling oils can be handled in the same equipment with equal ease. Be- 
cause of the auxiliary equipment required steam distillation cannot be 
recommended for all distillation. It is especially impracticable for the 
small producer in the field. Whenever conditions permit the construction 
of a suitably located, modern plant to. process raw material from a large 
area, such distillery should be equipped to carry on direct steam distillation. 

Before closing the general discussion of the three principal distillation 
methods, it should be mentioned briefly that each method can be modified 
by changing the pressure in the still. Accordingly, distillation can be car- 
ried out: 

(a) At reduced pressure ; 
(6) At atmospheric pressure ; 
(c) At excess pressure. 

The effect of these variations may be observed in the ratio of distillation 
(condensed) water to volatile oil. 

Any type of distillation carried out below the prevailing atmospheric 
pressure (usually with the aid of a vacuum pump) falls into class (a). 
Characteristic of distillation at reduced pressure is a low distillation tem- 
perature which has its limit only in the temperature of the cooling water 
and the efficiency of the condenser. The outstanding advantage of this 
form of distillation consists in the absence of the decomposition products 
resulting from heat. On the other hand, the vaporization capacity of high 



A. Water Dwtillatiou 

H. Water and Steam 

C. Steam Distillation 


Simple, low priced, port- 

Somewhat more com- 

If well constructed, usu- 

of Still 

able stills; easily in- 

plicated and higher 

ally more solid and dur- 

tailed in the producing 

priced than A. The 

able than A and B. Pos- 


smaller type is also mov- 

sibility of to rge size for 

able and may be in- 

large-scale distillation. 

stalled in the field. 

Type of 

Most advantageous for 

Well suited for herb and 

Suited for any charge ex- 


certain materials, es- 

leaf material. 

cept finely powdered ma- 


pecially when finely 

terial through which the 

powdered ; also for 

steam forms channels 

flowers which easily 

("rat holes"). Espe- 

lump with direct steam. 

cially well suited for 

Not well adapted for 

seed, root and wood ma- 

materials containing 

terials containing high 

saponifiable, water-sol- 

boiling oils. 

uble or high boiling 


Mode of 

Best results with finely 

Plant material must be 

Similar to B. 


powdered materials. 

uniformly but not too 


finely comminuted. 

Granulation gives best 

results with seeds and 


Mode of 

Material must be com- 

Material must be evenly 

Similar to B. Proper 


pletely covered by 

charged into the still. 

charging is very impor- 


tant; otherwise the 

steam channels through 

the plant material and 

low yield results. 


Good, if material is 


Good, if steam is slightly 


properly charged and 

wet. Distillation with 

moves freely in the 

superheated steam or 

boiling water. 

high pressure steam 

dries out the plant ma- 

terial, prevents diffusion, 

and causes a low yield of 

oil. Such distillation 

must, therefore, be fol- 

lowed with wet steam. 


Usually about 

Usually about 

Can be modified (high or 




low pressure steam), ac- 

Within the 

cording to the plant ma- 





A. Water Distillation 

B. Water and Steam 

C. Steam Distillation 


About 100. Care 

About 100. 

Can be modified (satu- 

Within the 

must be exercised not 

rated or superheated 


to "burn" the plant 

steam), according to 

material by contact 

the plant material. 

with overheated still 

walls. Vaporized 

water must be con- 

tinuously replaced. 


Conditions usually un- 

Hydrolysis fairly low, 

Conditions good, hydrol- 

of Oil 

favorable. High rate of 

provided no excessive 

ysis usually slight. 


ester hydrolysis. 

wetting of the plant 


charge by prolonged 

distillation and steam 

condensation within thi 

still takes place. 


Good, if plant material 

Good, if material is 

Conditions good, if plant 

Within the 

is kept covered with 

properly comminuted 

material is properly 


water and moves freely 

and charged. Pro- 

charged. Prolonged dis- 


in it. 

longed distillation 

tillation with wet steam 

causes excessive wetting 

causes excessive steam 

by steam condensation 

condensation within the 

and lumping of the 

still and lumping of the 

charge. Stills should 


be well insulated. 

Rate of 

Relatively low. " 

Fairly good. 



Yield of 

In most cases relatively 

Good, if no excessive 

Good, if plant material 


low, due to hydrolysis, 

wetting and lumping of 

is properly comminuted, 

also because water- 

the plant charge occurs. 

evenly charged, arid dis- 

soluble and high boiling 

This would prevent 

tillation properly con- 

oil constituents are re- 

steam from penetrating 

ducted. Lumping of 

tained by residual water 

the charge thoroughly 

the charge or steam 

in the still. 

and result in abnor- 

channeling might cause 

mally low oil yield. 

an abnormally low 

yield of oil. 

Quality of 

Depends upon careful 

Usually good. 

Good, if operation 


operation; "burning" of 

properly conducted all 

plant charge must be 


avoided, especially 

when distilling with 

direct fire. 


Distillation water in 

If properly separated, 

Similar to B. 


some cases must be 

the distillation water 

redistilled, or more 

can be discarded in 

conveniently returned 

many cases. 

into the still during dis- 

tillation (cohobation). 

Distillation waters con- 

tain products of hy- 

drolysis, chiefly. 


boiling substances, especially of those somewhat soluble in water, is con- 
siderably reduced. 

By inserting a valve into the gooseneck of the retort and by partly 
closing this valve during distillation, it is possible to throttle the outflow of 
the steam/oil vapors and to increase the pressure within the still. 13 Such 
distillation at excess pressure (0.5 to 1.0 atmospheres excess pressure, or 
1.5 to 2.Q atmospheres absolute pressure) is occasionally resorted to \n the 
essential oil industry, but its use remains very limited, because of the Result- 
ing decomposition of many oil constituents. 

(c) Equipment for Distillation of Aromatic Plants. The equipment re- 
quired for carrying on distillation of plant materials depends upon the size of 
the operation and the type of distillation to be used. There are, however, 
three main parts which, in varying size, form the base for all three types of 
hydrodistillation. A fourth part is necessary for any method of heating the 
still other than by direct fire. The three universally employed parts are : 

1. The retort, or still proper; 

2. The condenser; 

3. The receiver for the condensate. 

The fourth part consists of a boiler for generating steam. The latter is 
necessary for the process which, in the preceding discussion, we have called 
steam distillation, since direct live steam, often slightly superheated, is 
required, and this can be produced only in a separate steam boiler. In the 
case of water distillation, or water ami steam distillation, the still may be 
heated by direct fire but even here heating is frequently, and indeed pre- 
ferably, accomplished by steam jacketing the retort, or by means of closed 
(or occasionally open) steam coils. A separate steam boiler becomes in- 
dispensable, also, if any one of the latter heating methods, or a combination 
of them, is used. These four parts of the distillation equipment will be 
considered in order. 

The Retort. The retort, or still proper, commonly also called "tank/' 
serves primarily as a container for the plant material, and as a vessel in 
which the water and/or steam contacts the plant material and vaporizes its 
essential oil. In its simplest form the retort may consist merely of a cylin- 
drical container or tank, Avith a diameter equal to or slightly less than its 
height, and equipped with a removable cover which can be clamped upon 
the cylindrical section. On or near the top of the cylindrical section a pipe 
(gooseneck) is attached for leading the vapors to the condenser. For water 

13 For the sake of clarity, it should be mentioned that the injection of high pressure 
steam per se does not, to any marked degree, increase the pressure in a still, which, through 
its gooseneck and condenser, has a free outlet to the atmosphere. Unless throttled by a 
valve, or by too narrow a gooseneck, or by the heavy mass of tightly packed plant material, 
any excess pressure of injected steam is reduced almost at once to the atmospheric pressure. 



Perforated Bottom-. 

distillation this simple equipment is sufficient, since water and charge can 
be introduced, the cover put in place, and a fire simply built under the retort. 
For water and steam distillation a grid or false bottom is inserted sufficiently 
far above the real bottom of the still so that boiling water and plant material 
(the latter supported by the grid) do not come in contact. The water is 
brought to a boil either by a steam jacket or through a closed steam coil, 
or in simpler apparatus by a fire directly beneath the still. In the case of 
direct steam distillation the grid may be closer to the real bottom. Here 
live steam is introduced through a steam line, usually a perforated coil or 

cross below the false bottom. Such 
a simple retort, while entirely ade- 
quate, would be inconvenient to use 
because of the difficulty of removing 

r i~ - - ii t | le spent pl an t material. Fig. 3.5 

' ^ shows a drawing of this tyi>e of 


The cylindrical section, slightly 
tapered to facilitate application of 
the support rings, can be made of 
14-20 gage galvanized shoot metal 
depending on the size of the retort. 
For larger sizes, heavier metal 
(smaller gage number) should be 
used. This is bent to shape, soldored 
steam tight, and the circular bottom 
soldered on. Support rings, their number depending on the size of tho 
retort, are fastened outside and around the cylinder at 2 cr 2 ft. in- 
tervals, always with one at the top, and one at the bottom, of the 
section. Except for the top ring, these may be strap metal or angle iron, 
and in any case about 2 in. wide. The top support ring should be of 3-in. 
angle iron, to form a suitable contact surface for the cover. Just below the 
top support ring a 6- to 8-in. length of pipe is soldered to the side of the retort, 
to serve as a connection to the condenser. Frequently the gooseneck loads 
from the center of a convex or spherical top cover to the condenser, but the 
gooseneck should never be high, as it would then act us a sort of reflux con- 
denser. Any unavoidable vertical section of the gooseneck must be well 
insulated. This connecting pipe should be at least 4 in. in diameter and, 
if the rate of distillation is to be very rapid, may be even wider. Finally, 
just below the grid supporting the plant charge a steam inlet line, a 1-in. 
pipe, enters through the side of the retort. The distance between the bot- 
tom of the retort and the steam pipe must be large enough to permit any 
water condensing within the retort to accumulate at the bottom without 

FIG. 3.5. Galvanized iron retort 
for steam distillation. 




FIG. 3.6. Top view of gal- 
vanized iron retort showing 
crossed tee steam inlet on bot- 

contacting the steam pipe. To insure adequate steam distribution, the 
steam pipe inside of the retort should be arranged in the form of a coil or 
of a cross, as shown in Fig. 3.6, with small holes, about | in. in diameter, 
drilled in the top of each arm throughout its length. The total surface of 
these small holes should not be larger than 
the orifice of the coil or of the arms on the 
cross, as otherwise the steam will escape from 
the first holes without reaching the entire 
length of the coil or cross. In other words, 
the steam should be injected into the retort in 
such a way that it will be evenly distributed 
on the bottom of the retort and in rising will 
penetrate the plant charge uniformly. Larger 
stills are equipped with two steam coils, each 
with a separate steam valve. Prior to injec- 
tion, the steam is freed from excess water 
through a water separator. Years ago, it was customary to equip the 
steam stills, directly above the bottom, with a closed coil, for heating 
with indirect steam of high pressure. The idea was to keep the injected 
direct steam as dry as possible, by heating it through this closed (indirect) 
steam coil. Such precaution, however, is of doubtful value, because 
dissolved, nonvolatile extractive matter always drips from the plant charge 
to the still bottom, and is apt to "burn" and decompose in contact with 
the very hot indirect steam coil. Vapors of disagreeable odor are thus 
emitted, which might easily affect the .odor of the essential oil in the receiver. 
The bottom of the retort is provided with a drain valve sufficiently wide 
so that any water condensing within the charge and dripping to the bottom 
can be drawn off in the course of distillation. (This drain valve also serves 
as an outlet for the wash water, when the still is cleaned.) Otherwise such 
residual condensed water will accumulate and engulf the steam coil, with 
the result that the entering live steam will first have to pass through a layer 
of water, becoming wet in the process. In other words, instead of direct 
steam distillation we would then have a case of water and steam distillation. 
Wet steam has a tendency to wet the plant charge and agglutinate it. The 
advantages of direct steam distillation are thus lost. Whether or not this 
wetting takes place depends also upon the temperature and pressure of the 
injected live steam. At any rate, it is preferable continuously to remove the 
condensed residual water from the still bottom. The same result can be 
achieved by an automatic water separator (steam trap) attached to the still 
bottom. It is constructed in such a way that only water flows from it, 
but not steam. This steam trap should be installed in plain view so that 


its proper functioning is assured at all times. Steam traps are apt to lose 
their efficiency after a certain time and permit unutilized steam to escape; 
or they do not separate the condensed water effectively and more and more 
water accumulates within the still. This means an ever-increasing wetting 
of the plant charge in the still. Such a condition is recognized by a crackling 
noise and by trembling of the still. If there is no steam trap, a funnel 
should be attached beneath the outlet at the still bottom, and the water thus 
conducted away. Here, too, the water faucet is regulated in such a way 
that no unused steam escapes, and at the same time, no condensed water 
accumulates within the still. 

This arrangement completes the still proper. Needless to say, all joints 
must be soldered steam tight, as any steam leak represents loss of essential 
oil and fuel. 

Brief comment should be made about the top of the still and the goose- 
neck, i.e., the tube connecting the retort with the condenser. The old- 
fashioned convex or crane-like still heads are becoming obsolete and rare. 
The top of a modern retort is simply pierced, and a pipe inserted to serve 
as a gooseneck. The perfect still head is short and well insulated ; if convex, 
it curves gradually and tapers, so that it fits into the gooseneck. Any fancy 
designs, sudden turns, bends, or too narrow tubing must be avoided, as these 
would result in a throttling effect and in back pressure within the still. 

The gooseneck also is only slightly curved, and, gradually descending, 
leads from the retort directly into the condenser. It should not ascend, 
as this would give rise to considerable vapor condensation, the resultant 
liquid refluxing into the retort. A semicircular gooseneck, such as is some- 
times found on old stills, has a purpose only if high boiling and resinous 
constituents of an essential oil can, by its means, be condensed and returned 
into the retort. A gooseneck of this type, therefore, may be useful in the 
rectification of essential oils, but not in the distillation of plant material. 
In fact, these two operations must never be confused. Ascending and high 
goosenecks are excusable only if the distillation waters are purposely made to 
flow automatically back into the retort from the higher placed Florentine 
flask ; but in such a case the gooseneck must be well insulated. It usually is 
preferable to return the distillation waters into the retort by an injector, 
which measure makes high goosenecks superfluous. Furthermore, a high 
gooseneck produces a slight back pressure within the retort ; it must, there- 
fore, be amply wide. 

The retort cover shown in Figs. 3.6 and 3.7 may be made of sheet metal 
similar to that used on the retort. It should be strengthened and ringed 
with strap metal to coincide with the horizontal face of the top angle iron 
supporting ring on the retort. ^ 



Any suitable device for lifting the top may be used. Fig. 3.7 illustrates 
one such device, which can be attached easily. In order to avoid steam 
leaks between the retort and cover, they must be held tightly together with 
a suitable gasket, which may conveniently be a single piece of -in. to f-in. 
soft rope laid all the way around 
the top angle iron on the retort. 
Commercial gasket materials (as- 
bestos in rope form) give good service. 
The top and retort may be held to- 
gether by external clamps, or by bolts 
and washers, in which case the top 
angle iron on the retort and the outer 
ring of the cover must be suitably 
drilled with holes to accommodate 
the bolts. For best results bolts 
should not be more than one foot 

Another device occasionally used 
for holding the top to the retort con- 

Ty CunJenier 

FIG. 3.7. Top of retort. 

slats of a simple water seal or hydraulic joint (Fig. 3.8). It eliminates all 
clamps, and saves a good deal of labor, as the still top is easily hoisted in its 
place after the still has been charged, and can be removed with equal facility. 

However, the layer of water within the water 
seal must be sufficiently high to withstand any 
slight steam pressure developing within the 
retort; hence a water seal cannot be used 
when distilling with high-pressure steam. 
Also, some water evaporates from the seal in 
the course of the operation, for which reason a 
water seal is recommended for the distillation 
of grass or herb material, but not of roots or 
woods requiring long hours of processing. 
The false bottom or grid supporting the plant material may be a circular 
piece of coarse wire mesh, a tray perforated with many narrow slits, or a 
wooden platform made in the form of a lattice. In the distillation of seed 
material and, especially of crushed seed it will be necessary to cover the 
grid with sack cloth, or any other suitable coarse material, to prevent dust 
and fine particles from falling to the bottom of the retort and clogging the 
perforations on the steam coil. If the still serves for water and steam dis- 
tillation, the false bottom should be supported about 2 ft, above the bottom 
of the retort. In the case of direct steam distillation it need be only far 
enough above the bottom to clear the steam inlet line. Chains or heavy 

Fin. 3.8. Hydraulic joints 
or water seals between still top 
and retort. 



wires attached to three or four equally spaced points around the circumfer- 
ence of the grid may serve as handles so that the plant charge can be easily 
removed after distillation simply by lifting the grid. If charges in excess 
of 200 or 300 Ib. are to be distilled, it will be convenient to use more than one 
such section, placing a new one on top of the first layer and continuing the 
charge above this section. This arrangement prevents excessive packing, 
assures better steam distribution, and facilitates discharging the spent ma- 
terial, inasmuch as only a fraction of the total charge need be removed at 
one time. Coarser and specifically lighter material can be packed higher, 
whereas finer and heavier material should not exceed a certain height. 

To Condenser 

To Condenser 

Steam ^- 

FIG. 3.9. Sketches of two types of multi-tray retorts. 

Retorts serving for water distillation should be wider than they are high, 
so that the plant charge can be kept shallow, avoiding the pressure caused 
by the weight of a high charge. This will permit the comminuted plant 
particles to move freely in the boiling water, and assure quicker distillation 
and a better yield of oil. Retorts serving for water and steam distillation 
may be of approximately equal height and diameter. Retorts for direct 
steam distillation should be somewhat higher than they are wide so that the 
rising steam passes as much plant material as possible. As a rule, the di- 
ameter should be 6 to 8 ft. at the most ; if larger-scale operation requires a 
larger still capacity it is preferable to increase the height rather than the 
diameter of the retort. In this case it will be necessary to guard against 
excessive packing of the charge, which would cause uneven distribution of 
steam and excessive pressures near the bottom. When calculating the 
dimensions of a still one should keep in mind not only that some plant ma- 
terials are very voluminous but also that during distillation the mass often 
swells and expands by one-third of its original volume. The height of the 



retort in relation to its width depends upon the porosity of the plant material. 
A greater height is chosen for voluminous material, and shorter stills are 
preferred for more compact material. Excessive pressure can be avoided by 
a construction similar to that shown in Fig. 3.9. 

The screen or grid trays may be permanently installed at intervals of 2 
to 3, or 3 to 4 ft., according to the size of the retort, and each tray must then 
be filled or emptied individually through the 2-ft. or 3-ft. manholes. By 
supporting each section of the charge separately, excessive pressures ir any 
one section are avoided and packing is kept at a minimum. Care must be 
exercised to fill each tray with only a. relatively shallow layer, to insure a 
uniform distribution of material and, therefore, of the steam. This is 
particularly true of seed distillation, which requires much more experience 
and attention than distillation of herbs or leaves. 

FIG. 3.10. Use of baskets (perforated on bottom) for holding still charge. 

As pointed out above, the trays may also be movable, so that they can 
be lifted from the retort with chains or strong wire. For best results, the 
trays should not lie directly on top of the charge of the next lower tray but 
be separated by a space of 2 ft. or more, depending upon the size of the 
retort. This may be effected in several ways e.g., by supporting legs, 
or attaching all of the trays to a central vertical shaft on which the trays may 
be hoisted from the retort after completion of the operation. The principal 
precaution is to be sure that the steam actually penetrates the plant charge 
and does not find an easy passage along the side of the still wall. This may 
be prevented by coiling ropes around the outer edges of the various trays 
where they touch the wall of the retort. For the same reason, baskets are 
not generally to be recommended, particularly those with perforated sides, 



To Condenser 

such as wire baskets. The steam always follows the way of least resistance, 
and has a tendency to rise along and through the perforations of the wire 
meshing, between the walls of the basket and the retort. 

Baskets with walls of solid (not perforated) sheet metal and perforated 
bottoms are preferable (Fig. 3.10). However, these should fit quite tightly 
into the retort proper, leaving only a very small space between the walls 
of the basket and the walls of the retort. Even this small space, must be 
completely sealed with rope, so that the steam does not find an easy way 
from the still bottom to the top by passing outside the basket. If every 
precaution is taken, such baskets may be useful for the distillation of herb 
material; while one batch is being distilled, another basket outside of the 
still can be charged with plants and hoisted into the retort after the first 
basket has been lifted out. Also, the exhausted contents of such baskets 
can easily be dumped on a truck and carried away. 

In the case of the smaller stills, yet another method of discharging may 
be found convenient. The entire apparatus may be supported on trunnions 

located slightly above the middle of the 
retort. Distillation completed, the retort 
is disconnected from the condenser and 
steam line, the top removed, and the entire 
spent charge dumped out by rotating the 
retort about the trunnions. Fig. 3.11 
shows a typical arrangement. 

In years past most stills serving in 
our industry were constructed of copper. 
This metal has the advantage of durabil- 
ity; copper stills retain a certain value 
even after being dismantled, as the metal 
can be reworked. The inside of a copper 
retort, however, should be heavily tinned 
(lead-free tin!); this is true also (in fact 
more so) of the gooseneck and condenser. Otherwise the essential oils will 
contain copper, imparting to the oils a bluish-green color which must be re- 
moved before the oil is acceptable to the trade. Sheeted aluminum also can 
be used for the construction of stills, giving satisfactory results except with 
phenol-containing oils (phenols attack aluminum). Today most retorts 
serving for large-scale steam distillation of plant material are made of gal- 
vanized sheeted iron, which renders good service for our purposes. Tinned 
copper is still being favored for equipment used in the water distillation of 
aromatic plants, and for apparatus employed in the redistillation, rectifica- 
tion or fractionation of essential oils. Some retorts in more primitive 
countries are made of wood ; if solidly constructed they cannot be condemned, 

- .,j Tilted Position 

FIG. 3.11. Tilting still on trunions. 


but should be used always for distillation of only one type of plant material. 
Wood has a tendency to absorb a little essential oil, which cannot be re- 
moved even by the most thorough washing and boiling with lye. Hence, 
a certain odor always adheres to wooden retorts which might easily spoil 
the odor of another type of oil, if the latter were distilled in the same 
wooden retort. 

Insulation of the Retort. In all cases the retort, including the top, 
should be well insulated to conserve heat. This holds true particularly of 
stills exposed to cold air, wind and draft. If insulation is neglected, exces- 
sive condensation of steam within the retort will occu as n, result of heat 
losses from its surface. This causes undue wetting of the charge, lumping 
and agglutinating of the plant particles, excessive steam consumption, pro- 
longed distillation, and, usually, an inferior yield of oil. For small portable 
units, considerable insulation can be afforded by surrounding the retort 
with a jacket made of wooden planks and held in place by wire. The inter- 
space may be filled with powdered cork or sawdust. Much better insulators 
are asbestos and magnesia. Either of these can be applied directly to the 
retort in the form of a very thick paste in water, which dries to a hard ad- 
herent layer. Three to six inches of this material will suffice for most 
economic operation. 

A high grade of insulation of this sort appears particularly important in 
large installations, where much steam is required. There, all heated sections 
and steam lines should be well insulated to prevent escape of heat, which 
represents an unnecessary expense. Probably the most effective insulation 
material is asbestos, which, in the form of bricks or pipe covering, can be 
suitably fastened to the still and pipes, or, in the form of powder, can be made 
into a thick paste with water. This paste may be applied with a trowel to 
the parts to be insulated. A paste made from ground kieselguhr, water and 
animal hair, if available, also serves as insulation. In any case, such an 
insulating layer should be about 2 in. thick. Von Rcchenberg 14 suggested 
the following method of insulating stills and steam pipes : 

"Fifty liters of calcined kieselguhr, ten liters of gritty ground 
cork waste, and three handfuls of clear pulled pigs* or calves' 
hair are thoroughly mixed. A thin, hot, stirred soup of rye, 
wheat, or corn flour is added, to make a viscous, stiff mash. 
Stones of brick size and strength are then formed and dried on 
the steam boiler or elsewhere. These bricks serve to cover the 
stills and steam armatures after they have been covered with a 
viscous flour soup. If necessary, the bricks are held in place by 
iron straps. The whole cover is smoothed, and the joints and 
grooves are filled with a mash of calcined kieselguhr. Finally, 
cheap, thin fabric is pasted on top and painted over twice with 
oil paint." 

14 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig (1910), 599. 


Very hot steam pipes are more advantageously covered with asbestos 
fiber. The joints of the steam armatures, which are best made with flanges, 
should not be insulated. 

Charging of the Still. The problems of charging a retort with plant 
material, and of discharging' it, are more important than is usually realized, 
and should be attacked by considering the labor involved. Any labor sav- 
ing device might mean considerable economy in the final calculation. As a 
rule the plant material should be transported (trucked, hauled, etc.) as 
near as possible to the still. If the material has to be comminuted, the 
machines should be located near-by, if possible on a floor or platform above 
the stills, so that the comminuted material falls or slides by gravity into the 
retort. The old-fashioned way of charging and discharging with pitchforks 
and shovels is costly, and, although the initial cost is high, a conveyor belt, 
or a small crane, will soon pay for itself and in general speed up the operation. 

The Condenser. We shall now proceed to a description of the condenser, 
the second major part of the distillation equipment. Here again the size 
and design are variable, and several typical cases will be considered. The 
condenser serves to convert all of the steam and the accompanying oil vapors 
into liquid. This requires the removal of an amount of heat equivalent to 
the heat of vaporization of the vapors plus steam, and a small additional 
amount of heat to cool the condensed material (condensate) to a convenient 
temperature below its boiling point. The rate at which heat will be removed 
from the vapors is expressed by 

q = UA&t 

in which : q = heat removed per unit time ; 

U = a constant depending on operating conditions ; 
A = the area available for removal of heat ; 

A = the temperature difference between the hot vapors and the 
cooling medium. 

The scope of this work does not permit a full discussion of all factors 
that affect the value of U. Several of them will be considered in the dis- 
cussion of condenser operation. Probably the most important ones are the 
rate of flow of the cooling medium (cold water) past the heating surface, 
the rate of flow of the vapors, and the material of which the condenser is 
constructed. The value of U increases as these factors increase, and this 
fact should always be borne in mind when constructing a condenser. The 
area available can be made as large or as small as desired, but it is evident 
from the above relation that the total capacity of a condenser, and therefore 
of a still, will be directly determined by the area used. The temperature 
difference can be controlled by the temperature of the cooling medium (here- 
inafter referred to as water, since water is by far the most commonly used 



cooling medium) because the temperature of the vapors is fixed within rather 
narrow limits by the distillation itself. Fig. 3.12 shows the simplest type 
of condenser, now seldom used, and described here chiefly for its historic 



First Catch 


Pei f 01 a led 



FIG. 3.12. Sketch of an old-fashioned zigzag condenser. 

Water is fed to the overhead reservoir from which it flows to a distributor 
trough which consists simply of a shallow pan with a perforated bottom. 
This permits the water to trickle over the entire length of the condenser 
tubes. The water may be caught in an intermediate catch pan, as shown, 
and a second distributor installed to insure efficient condensation. It will 
be noted that the condenser tubes are all sloped downward slightly, to insure 
proper drainage of the condensed oil and steam. Also the size of the con- 
denser tubes becomes smaller as the cold end is approached. In order to 
avoid excessive back pressures being built up in the still, it is necessary to 
use fairly large tubes to accommodate the vapors immediately after they 
leave the retort. Since the volume of the vapors, and, therefore their ve- 
locity, decreases rapidly on cooling, as a result of condensation, the size of 
the condenser pipes can be reduced proportionately. In Fig. 3.12, for ex- 
ample, the first two tubes may be 4-in. pipe, the next two 3-in. and the re- 
mainder 2-in. A 4-in. pipe coming from the still will accommodate up to 
700 Ib. per hr. of condensate (about 85 gal.), in so far as the development of 
back pressure is concerned. The length and number of tubes to be used 
will be determined by the amount of vapor to be condensed. An estimate 
of the pipe area required can be made by using a value of 40 for the factor U 
in the above equation. The temperature difference will be equal to the 


average value of the difference between 212 F. (100 C.) (the temperatuer 
of saturated steam at ordinary pressure) and the temperature of the water 
in the first and second troughs. For example, if the fresh water in the top 
trough is 60 F. (15.56 C.) and the water in the first catch trough is 90 F. 
(32.22 C.), the temperature difference to be used would be the mean of 
(212 - 60) and (212 - 90) or 137 F. The value of q, the amount of heat to 
be removed, can be calculated approximately by multiplying the number of 
pounds of condensate per hour by 1,000. The pipe area required will then 
be given in square feet. By connecting two or more such zigzag sections in 
parallel, the same cooling water system can be used for all of them, thus 
increasing their capacity, conserving height and permitting the use of shorter 
tubes for a given amount of condensation. 

Another very simple and inexpensive type of condenser consists merely 
of a series of long pipes, usually 2 in. in diameter, laid horizontally in a 
trough through which water flows. Four 2-in. pipes will have the same 
vapor capacity as one 4-in pipe as given above, but will offer considerably 
more cooling surface. Since the value of the factor U in both of these 
cases is somewhat lower, the length of the pipes must be proportionately 
greater. Again, the pipes should have a definite slope toward the cool end, 
to insure adequate drainage of the condensate. 

The above described methods of condensing vapors, although cheap 
and entirely satisfactory, lead to rather awkward and bulky construction. 

The most commonly used condenser is that in which coils are inserted 
into a tank supplied with running cold water, which enters from below and 
flows against the steam and oil vapors. In order to utilize the cooling water 
more effectively, it is advisable to insert two adjoining coils into one con- 
denser tank. Fig. 3.13 shows a coil condenser. 

In an even more satisfactory condenser arrangement, advantage is taken 
of the fact that a more rapid flow of cooling water results in more efficient 
cooling. The condenser tubes are assembled in a single vertical bundle, 
the number and length depending on the amount of condensation to be 
accomplished, in such a way that the vapors to be condensed enter the tubes, 
and cooling water circulates around the tubes. Fig. 3.14 shows a typical 

Condensers of this type are available ready built from any equipment 
supply house, and should be purchased from such a specialist. The con- 
struction of a satisfactory leak-proof tubular condenser presents an exceed- 
ingly difficult problem for an unskilled workman. The factor U for such a 
condenser will usually be about 200 ; thus, for a given amount of condensa- 
tion and a given cooling water temperature, only one-fifth of the area re- 
quired in a zigzag condenser will be required. Tubular condensers should 
be used in a vertical position with vapors entering the top and condensate 



leaving the bottom. Connection with the retort must again be of adequate 
size to avoid excessive back pressure in the still. Tubular condensers not 
only are more efficient and require much less space than spiral condensers, 
but they also permit easier and more thorough cleaning. If possible they 
should be fed with soft water to prevent the formation of scale (incrustation), 
which reduces the exchange of heat, and necessitates frequent ck-tning. 

Fir,. 3.13. Coil condenser. 


FIG. 3.14. Tubular condenser. 

It is always better to construct the condenser a little too large rather 
than too small. Longer tubes or coils require less cooling water, as the 
contact with the vapors and with the flowing condensate lasts longer and 
permits the absorption of more heat, so that the temperature of the con- 
densate at the end more closely approaches that of the inflowing cooling 
water. At any rate, the condenser surface must be large enough to cool the 
distillate sufficiently, even at a very high rate (speed) of distillation. Slow 
distillation has many disadvantages, such as hydrolysis of esters, wetting, 
agglutination and conglomeration of the plant charge, frequently with a 
concomitant ly low yield of oil. 

The cooling water in the condenser tank does not need to be cold from 
top to bottom ; such a condition, on the contrary, is rather a disadvantage, 


because too rapid and excessive cooling of the steam/vapor mixture causes 
the distillate to run off the condenser unevenly or jerkily. For this reason, 
the condenser tank should be fed with only as much cold water as is neces- 
sary to condense the vapor mixture and to cool the condensate sufficiently 
a factor depending also upon the type of oil produced. The maximum effi- 
ciency of a condenser is attained when the condensate has been cooled to a 
sufficiently low temperature by heat transfer to the cooling water, which 
then flows out at a temperature approaching that of the incoming vapors. 
This effect, however, is rarely achieved. Usually it suffices if the cooling 
water flows out at a temperature of 80 C. (about 175 F.) and if the distil- 
late has a temperature of 25 to 30 C. (77 to 86 F.). 

If the ratio between condenser surface and heating surface (in the still) 
is correctly maintained the condenser will permit rapid distillation. But if 
the condenser surface is too small and in many of the small field distilleries 
this is true the rate of distillation must be adjusted to the efficiency of the 
condenser. Distillation must then be slow, and this, as pointed out, in- 
volves many disadvantages and inadequacies. Otherwise, the vapors blow 
at high speed through the condenser coils or tubes, which are too short for 
complete condensation of the vapors or for sufficient cooling of the conden- 
sate. Considerable oil may then be lost by evaporation. 

The condenser tubes or coils must be made of heavily tinned copper, of 
pure tin, aluminum, or stainless steel, if discoloration of the oil by iron or 
copper is to be prevented. Aluminum, however, cannot be used with oils 
containing phenols. 

If distillation is to be carried out at reduced pressure, the tubes or coils 
must be made strong enough to support a pressure differential of one at- 
mosphere without letting water seep from the condenser tank into the con- 
denser. This is particularly important in the case of oil distillation (rectifi- 
cation, fractionation) in vacuo. Condensers serving for distillation at 
reduced pressures should also be sufficiently wide to permit an unhindered 
flow of steam and vapors, as any throttling by too small a diameter in- 
creases the pressure within the still in other words, creates back pressure. 
As a general principle in the construction of distilling equipment it should 
be kept in mind that the steam and oil vapors should flow easily and smoothly 
through the system, without encountering any sharp bends or curves in 
the tubes. 

A wire screen, inserted between condenser and gooseneck, prevents 
plant particles lifted up by live steam from entering the condenser tubes or 
coils. As the wire screen may become clogged, and would then cause an 
explosion in the still, the retort should be provided with one or two efficient 
safety values. 



The Oil Separator. The third essential part of the distillation equipment 
consists of the condensate receiver, decanter or oil separator. Its function 
is to achieve a quick and complete separation of the oil from the condensed 
water. Since the total volume of water condense i will always be much 
greater than the quantity of oil, it is necessary to remove th^ u r ator con- 
tinuously. The condensate flows from the condenser into the oil sepaiator, 
where distillation water and volatile oil separate automatically. Many 
separators are constructed according to the principle of the ancient 1 loren- 
tine flask, hence, are often called Florentine flasks. Volatile oil and water 
are mutually insoluble; because of the difference in their specific gravities, 
the two liquids form two separate layers, the usually specifically lighter oil 
floating on top of the water. Whenever the specific gravity of the oil is 
greater than 1.0, the oil sinks to the bottom of the separator. The design 
of the receiver should permit the removal of water whether the oil being 
distilled is heavier or lighter than water. 

For oils 
lighter than water 

heavier than water 

FIG. 3.15. Florentine flasks. 

Smaller Florentine flasks arc made of glass, larger separators (about 15 
liters and more) of metal usually tin, tinned copper, aluminum or gal- 
vanized iron. For all-around use, heavily tinned copper vessels are most 
practical. Lead must not be employed, as oils containing free fatty acids 
would form lead salts, which might cause poisoning if the oil were used 
internally. Rubber tubing or rubber stoppers cannot be used because rub- 
ber, being partly soluble in essential oils, gives to them an objectionable 
odor. Fig. 3.15 shows two oil separators, one for oil lighter than water, and 
one for oil heavier than water. 

Another and quite satisfactory type of receiver operates according to the 
following principle: 

A cylindrical or rectangular vessel is divided into two chambers by a 
partition which ends a few inches above the bottom of the vessel. The two 



Oil and Water 

chambers are connected with one another. The distillate flows into the first 
chamber, while the distillation water runs off through a tube on the second 
chamber. Oil lighter than water collects in the upper part of the first 

chamber and flows out from there, while oil 
heavier than water sinks to the bottom of 
the two chambers and is drawn off from 
there. Fig. 3.16 shows an oil separator of 
this type. 

Oil and water often do not separate im- 
mediately in the oil separator, especially if 
the differential between the specific gravities 
of water and oil is slight. The distillate 
must not, therefore, flow too rapidly, and 
any turbulence in the liquids must be 
avoided ; in other words, the separator must 
be large enough to permit water and oil to 
separate as completely as possible. Other- 
wise droplets of oil will be carried away with 
the outflowing water. A smooth flow of the 
distillate can be assured by inserting a long- 
stemmed funnel into the separator, the lower 
outlet of the funnel being turned upward. 
The distillate streaming from the condenser 
thus flows first through the funnel, without 
disturbing the oil layer, and the oil droplets 

FIG. 3.16. Oil separator for 
oils lighter and/or heavier than 

rise slowly from the orifice of the funnel toward the oil layer, in which they 
dissolve. If, on the contrary, the distillate is permitted to run from the con- 
denser directly into the oil layer, the distillation water exerts a dispersing ef- 
fect on the constituents of the oil having a specific gravity close to that of 
water: a sort of suspension will result. It should be a general rule to 
separate the oil layer from the water as quickly as possible, and to avoid 
any agitation of the two media. 

If the single oil separator is not large enough, several should be em- 
ployed, connected serially, usually in the form of step-like cascades, each 
of the separators being placed a little lower than the one that precedes it, 
so that oil and water will separate clearly in the last and lowest vessel. 
Occasionally, distributing bridges are used, in which the distillate flowing 
from the condenser is distributed into several oil separators. 

Some plant materials yield oils which distill over first in fractions lighter 
than water, and in the later course of distillation, in fractions heavier than 
water. This is caused by a progressive increase in the specific gravity of 
the oil fractions. In such cases, two types of oil separators must be em- 



ployed : the first for separating any oil lighter than water, and the second, 
connected with the first, for separating any oil heavier than water. The 
same distillate thus flows through both separators, 01 the two-chamber 
separator described previously can be used to advantage. 

The oil and water separator shown in 
Fig. 3.17 offers the advantage of combin- 
ing several features in a single unit : 

The water outlet is placed as far away 
from the oil layer as is possible. 

For oils lighter than water, the oil is 
drained at A ; valves B, C, and D are 
closed ; and water is taken off at E through 
the automatic drain. 

For oils heavier than water, the oil is 
drained at #; valves A, D, and E are 
closed ; and water is taken off at C through 
the automatic drain. 

For oils separating into two fractions, 
one heavier and one lighter than water, 
the lighter oil is taken off at A ; the 
heavier oil is taken off at B ; valves C and 
E are closed; and water is taken off at 
D through the automatic overflow. 

Some oils (e.g., rose oil) deposit sepa- 
rate crystals when cooled below a certain 
temperature. Such oils are liable to clog 
the condensers if the distillate flows too 
cold. In this case it is necessary to let the distillate run tepid by reduc- 
ing the volume of cooling water entering the condenser tank. 

Obviously the separation of two insoluble liquids takes place more 
quickly and more completely the wider the differential between their specific 
gravities. Therefore, oils or fractions of oils which have a specific gravity 
only slightly below that of water do not readily separate from the distilla- 
tion water at room temperature, but form milky suspensions or emulsions. 
In such cases, the distillate must be forced to run warmer from the con- 
denser into the Florentine flask, because with rising temperature the specific 
gravity of the oil decreases relatively more than that of the water. The 
resulting greater differential in the specific gravity between the oil and 
water at elevated temperature causes the two layers to separate more readily. 
If, on the other hand, the specific gravity of an oil at room temperature is 
slightly higher than that of water (oils heavier than water), the distillate 
than Water 

FIG. 3.17. Oil and water separator for 
oils lighter and/or heavier than water. 


should run as cold as possible. Any increase in the temperature, in this 
case, would further decrease the already small differential between the 
specific gravity of the oil and that of the water, and separation of the two 
layers would become even more difficult, if not impossible. 

This, however, is the exception. As a general rule, and in the case of 
most essential oils, the temperature of the condensers should be kept as 
low as possible in order to prevent evaporation and loss of oil. 

The separated oil is finally set aside until suspended water droplets 
and solid or mucilaginous impurities have separated, when it is filtered clear 
and stored in well-filled, airtight containers in a cool, dark cellar, or in an 
air-conditioned room. 

It should be remembered that the condensed water will always be satu- 
rated with oil. Discarding this water means a loss in yield of oil. In the 
case of water distillation or water and steam distillation this condensed 
water may be used again as the water supply for the next charge of the same 
type of plant material, or the distillation water may be returned into the 
still and redistilled (cohobated) during distillation. For this purpose the 
oil separator (Florentine flask) must be installed sufficiently high above the 
still so that the pressure of the flowing distillation water may overcome the 
slight pressure usually prevailing within the still. In order to avoid ex- 
cessive height of the gooseneck, the condenser can be set up side by side with 
the still, the distillation water then being pumped or injected into the still 
with a steam injector. This procedure prevents loss of oil, since the oil in 
the water simply means an additional volatile oil charge to the still. It has 
been suggested that the condensed water be returned to the steam generat- 
ing equipment (boiler), but this idea cannot be recommended because of the 
difficulties encountered with the boiler, and also because of the heat in the 
steam boilers, which would have a deteriorative effect upon the quality of 
the dissolved oil. In the case of direct steam distillation, the dissolved oil 
is recovered through redistillation (cohobation) of the distillation water, or 
through extraction with volatile solvents, both of which will be discussed 
later in more detail. 

Steam Boilers. Before leaving the subject of equipment, we must make 
brief mention of the use of auxiliary boilers when water and steam distilla- 
tion, or steam distillation is used. The size of the boiler will depend on the 
amount of steam required ; no generalization can be made. Because of the 
danger involved in the operation of a steam boiler, it is recommended that 
such equipment be purchased from an established dealer in power genera- 
tion equipment. Briefly, besides the usual fire box and tube heater, the 
system should include gages for determining w'ater level and pressure, 
safety valves to guard against operation at too high pressure, a pump or 
injector for circulating the water, and all necessary piping for the particular 


operation at hand. The supplier should be consulted before ordering any 
equipment. All reputable suppliers maintain well-trained engineering 
staffs for the purpose of analyzing customers' requirements, and advantage 
should be taken of this service. 

There are two types of boiler, viz., the so-called low-press j re boiler, 
developing 40 to 45 Ib. of pressure, as measured at the boiler gage, and the 
high-pressure boiler, which develops a steam pressure of approximated 100 
Ib. and more. High-pressure steam is used to attain higher temper it ares 
rather than merely to force the steam through the plant riateri:.! contained in 
the retort. Theoretically the temperature of saturated steam is a function 
of the steam pressure. Steam, as developing from boiling water (pressure 
at the gage = 0), has a temperature of 212 F. (100 C.) ; at 40 Ib. it has a 
temperature of 287 F. (141.7 C.) and at 100 Ib., 338 F. (170 C.). Steam 
of low pressure and, therefore, of comparatively low temperature, is likely 
to be recondensed to water in the lower part of the plant charge, whereas 
steam of higher pressure and temperature penetrates the plant material 
more effectively and with less condensation in the still. High-pressure 
boilers are, therefore, more efficient in regard to distillation, shortening its 
length. On the other hand, it is claimed that low-pressure steam, as a rule, 
yields more alcohol soluble oils, free of bitter resinous matter. 

In actual operation low-pressure boilers produce little pressure but 
a large volume of steam. They are constructed of appropriate gage sheet 
metal with cast-iron beads. Even the flues are made of galvanized sheet 
metal. All of the other boilers are "high pressure." It is true that some 
distillers use 30 to 100 Ib. of pressure, but that depends on the steam require- 
ments. Data collected by experts of Purdue University, Lafayette, In- 
diana, on retort temperatures in the distillation of peppermint oil, show that 
there exists little difference between the temperature of the trays at 20 Ib. 
and at 80 Ib., but the speed with which the distillation takes place is an 
important factor economically. The explanation is obvious if one considers 
that the steam is released into a large retort, not under pressure. There 
the steam temperature will be reduced to the still temperature immedi- 
ately without pressure. In some cases, of course, the steam is "pushed" in 
so fast that a slight back pressure results, but this will seldom cause more than 
a 10 F. (about 5 C.) rise above 212 F. (100 C.) in the still. 

If superheated steam is to be used, a superheater of one form or another 
must be installed. One method 16 of superheating steam consists of permit- 
ting high-pressure, dry saturated steam to expand suddenly to a lower pres- 
sure through a well-insulated valve. This will result in a moderate amount 
of superheating, at least theoretically speaking. A well-designed boiler 

15 For theoretical explanation, see von Rechenberg, "Theorie der Gcwinnung und 
Trennung dcr atherischen Olc," Leipzig (1910), 400. 


should produce very nearly saturated steam and the above method will, 
therefore, result in slight superheating. If the steam as generated is very 
wet, it will be necessary to do one of two things in order to accomplish super- 
heating. One method consists of installing in the high-pressure line a water 
separator, which will remove most of the liquid water from the steam. This 
dried steam may then be expanded as described above to produce super- 
heated steam. An alternative method is to expose the line carrying wet 
or saturated steam to a temperature sufficiently above the boiling point of 
water at the steam pressure to permit the extent of superheating desired. 
This can be accomplished by running the steam line through a region in 
which the waste gases from the boiler can transfer part of their heat to the 
steam. The amount of exposure must be carefully controlled, to avoid ex- 
cessive superheating. If desired, this heating may also be done in an en- 
tirely separate unit, and since the stack gases always contain waste heat, 
this might just as well be recovered. In the installation of superheating 
equipment, the boiler supplier can again be of great assistance. 

(d) Practical Problems Connected with Essential Oil Distillation. 
At this point it is advisable to devote space to a few practical suggestions 
for the operation of essential oil stills. Many of the points brought out in 
the following paragraphs have already been mentioned, but it appears de- 
sirable to emphasize them, since failure to adhere to them may well repre- 
sent the difference between successful and unsuccessful operation. The 
three general methods of conducting steam distillation will be considered in 

Water Distillation. Let us first consider the operation of a water dis- 
tillation system. In every method of plant distillation, whether steam dis- 
tillation, water and steam distillation, or water distillation, only those 
quantities of the essential oil with which the steam comes in direct contact 
can be vaporized. Any oil held within the plant tissue must first be ex- 
tracted from the glands and brought to the surface of the plant by osmosis. 
But the forces of hydrodiffusion work very slowly whenever the distances 
to be bridged are relatively long. Water distillation necessitates a thorough 
comminution of the plant material to the smallest possible size; in other 
words, the reduction must exceed that required for direct steam distillation 
or water and steam distillation. All interspaces between the plant particles, 
which in the case of water distillation are filled with water, must be pene- 
trated continuously by rising steam. 

The retort is charged with the plant material to be distilled, and sufficient 
water added to fully cover the entire charge, leaving, however, ample vapor 
space above the charge to avoid boiling over and carrying over of spray into 
the condenser. After the cover has been fastened tightly using a suitable 
gasket between cover and still to avoid loss of vapors at that point the 


retort is connected to the condenser, and the cooling water permitted to 
flow through the latter. The fire is then started, if a direct fired still is being 
used, or the steam line opened, if either a steam jacket or steam coils are 
used for heating. Once the charge has reached its boiling point at the par- 
ticular pressure used, condensate will begin to issue from tjie open end of the 
condenser, and should be run directly into the separator, which was pre- 
viously filled with water. The rate of distillation can be controlled by the 
intensity of the fire, by the pressure in the steam jacket, or by the rate of 
introduction of steam. With direct fire, special care must be taken to avoid 
overheating the plant material. As the water and 01' evaporate, part of 
the charge will soon cease to be covered with water, and hence no longer will 
be automatically protected from overheating. It may be advisable to add 
more water as the distillation proceeds, to prevent any part of the charge 
from becoming exposed to the full heat of the fire. When a steam jacket 
or closed steam heating coils are used, there is less danger of overheating 
unless the water level falls below the top steam coils. Here again the addi- 
tion of sufficient water will prevent such an undesirable result. With open 
steam coils this danger is largely avoided, since for every pound of steam 
injected, a pound of steam condenses as distillation water in the condenser. 
However, care must be taken to prevent accumulation of condensed water 
within the retort, or the water level will rise gradually to the top. There- 
fore, the still should be well insulated and not exposed to draft or cold wind. 
Furthermore, the water charged into the retort at the beginning of the 
operation should be hot, as cold water would condense too much of the 
injected live steam. 

The rate of distillation must be adjusted to suit the particular equip- 
ment and material being distilled. This rate should, of course, be main- 
tained near the maximum in order to obtain the maximum production of oil. 
There are other, perhaps less apparent, reasons for maintaining a rapid rate 
of distillation when using water distillation. Principal among these is the 
fact that only by rapid distillation can the charge be maintained in a suffi- 
ciently loose condition to insure thorough penetration of the plant material 
by the rising steam. Steam which does not contact the charge, for example 
steam generated at the water surface as in a slow distillation, cannot carry 
any essential oil with it, and will be wasted. A lively conduct of distillation 
prevents to a large extent undesired agglomeration of the plant material, 
and brings about a more effective contact area between charge and steam. 
This in turn causes not only an increase in the rate of production, but also 
a better total yield of oil. It is commonly assumed that during water dis- 
tillation all parts of the plant charge are kept in motion by boiling water. 
This, however, is only partly true. Steam bubbles form mainly along the 
closed steam coils, along the heated bottom and walls of the retort, and rise 


to the surface by the shortest way, avoiding any obstacles. Provided the 
distillation material is charged loosely and remains loose in the boiling water, 
the steam bubbles probably will contact all plant particles quite evenly and 
vaporize their volatile oil. This is the case especially with woody material, 
but flowers have a tendency to agglutinate under the influence of steam and 
form large lumps. True, the volatile oil diffuses quite readily from tender- 
walled epidermis glands, but when leaves or flowers cling together diffusion 
is slowed down. Distillation must then be accelerated to a point where all 
particles of the plant charge are agitated and kept in continuous motion by 
rising and exploding steam bubbles. The degree of comminution, the weight 
of the plant charge and the construction of the still should be calculated ac- 
cordingly. Plant material which contains an essential oil composed of high 
boiling constituents can be exhausted by water distillation only if com- 
minuted to small particles. 

Von Rechenberg pointed out that many years ago distillation was carried 
out almost exclusively over direct fire, water distillation then being the rule, 
steam distillation the exception. Experience had been that complete ex- 
haustion of many plant materials could be effected only under great diffi- 
cujties and after several days of distilling. Extraction of oil of cloves, for 
instance, seems to have caused a great deal of trouble. Directions dating 
back to the middle of the last century claim that cloves could be exhausted 
only by repeated distillation; in other words, the retort had to be opened 
from time to time, the content stirred, and the evaporated water replaced. 
In the case of cloves this was repeated from three to eight times. Very 
probably the plant charge relative to the size of the still was much too large 
and distillation had to be carried out much too slowly with a small fire; 
otherwise the cloves in the still would have foamed over into the condenser. 
Small-scale operators, especially field distillers employing directly fired 
retorts, still commit the mistake of not putting sufficient water into the 
retort. Ignorant of the simple rules underlying water distillation, they 
seem, to prefer a slow distillation, or they are handicapped by too small 
condensers, or by lack of water. Frequently they add to the plant material 
such a small quantity of water that only the still bottom, which is directly 
fired, remains covered with water at the end of the operation. This practice 
is faulty. Plant parts rising above the level of the boiling water in the course 
of water distillation tend to lump together, to become almost impenetrable 
for steam, and therefore not to yield their oil completely. For this reason, 
the retort should be only partly filled with plant material, which should 
remain fully immersed in water, even when distillation is completed. Only 
by following this precaution is it possible to exhaust the plant charge by 
water distillation, as far as this can be done at all. 


Water distillation is still quite widely used with portable equipment in 
primitive countries. There, lack of roads and poor transport facilities 
prevent hauling of the plant material from outlying growing regions to 
centrally located distilleries. Therefore, the apparatus must be moved into 
the growing sections, or in other words, follow the plant material. Small 
stills, simple, sturdy and low priced, hence retain the favor of ira-iy native 

Aside from these purely practical conveniences, water distill aiion 
possesses one decided advantage. It permits processing of very finely 
powdered material (root, bark, and wood, etc.) or of p*'iut parts which by 
contact with direct (live) steam would easily agglutinate and form lumps 
through which the steam cannot penetrate (e.g., roses or orange blossoms). 
From such an agglutinated mass, live steam vaporizes the oil only from the 
outside and not from the inside. Steam distillation, therefore, would re- 
main incomplete. The nascent steam bubbles attack all parts of the plant 
charge only if the latter moves loosely and freely in boiling water. As a 
matter of fact, material which readily agglutinates can be processed only by 
water distillation. 

On the other hand, water distillation suffers from several disadvantages. 
Whether comminuted or not, the plant material cannot always be completely 
exhausted. Furthermore, certain esters, linalyl acetate, for example, are 
partly hydrolyzed; other sensitive substances, such as aldehydes, tend to 
polymerize under the influence of boiling water, etc. Consequently, all 
other conditions being the same, the quality of product from a rapid dis- 
tillation will be better, in general, than that of the product from a slow dis- 
tillation. Water distillation requires a greater number of stills, more space, 
and more fuel. It demands considerable experience and familiarity with 
the method and its effect, in fact more experience and care than any other 
form of plant distillation ; otherwise the yield of oil will be affected and fall 
considerably below that obtained by water and steam distillation or by 
direct steam distillation. Water distillation is the least economical process, 
water and steam distillation giving, in general, better results in the case of 
field distillation. 

Another peculiarity of water distillation lies in the fact that high boiling 
and somewhat water-soluble oil constituents cannot be completely vaporized 
from the large quantities of water which must cover the plant charge in the 
still, or they require so much steam that they can be recovered only partly 
from the distillation (condensed) water; therefore, the distilled oil will be 
deficient in regard to these constituents. In other words, distillation re- 
mains incomplete. Such compounds are high boiling alcohols (phenyl- 
ethyl alcohol, cinnamyl alcohol, benzyl alcohol, etc.), phenols (eugenol, 
etc. ), certain nitrogenous substances^ and some acids. \ typical example 


is orange blossom oil : the methyl anthranilate present in the flowers cannot 
be completely recovered by distillation, extraction with volatile solvents 
giving better results. The case is similar with roses : distilled rose oil lacks 
the somewhat spicy note of the extracted product (concrete or absolute) and 
contains much less phcnylethyl alcohol, because eugenol and phenylethyl 
alcohol, as the author 16 proved, remain in the residual still waters. How 
much of these high boiling, somewhat water-soluble compounds are actually 
carried over by distillation depends upon their boiling points, their degrees 
of solubility in water, and the quantity present in the plant material. If 
the plant charge, despite comminution, contains coarser particles, which 
during the boiling do not soften and, therefore, are not torn apart, these 
particles will retain high boiling, water-msoluble oil constituents, because 
diffusion through the greatly swollen tissue layers acts too slowly. These 
factors explain why essential oils obtained from the same plant material by 
water distillation or by steam distillation vary considerably in regard to 
yield, physical properties and chemical composition. 

For all these reasons, water distillation is used today in essential oil 
factories and for large-scale production only in cases where the plant material 
by its very nature cannot be processed by water and steam distillation or, 
even better, by direct steam distillation. 

For most efficient operation, a modern retort serving for water distilla- 
tion should be flat and wide, thereby offering a large surface of evaporation. 
The plant material should be filled in evenly, not higher than 4 in. Water 
is then pumped into the still until it stands about 2 in. above the charge. 
Steam of at least 3 atmospheres absolute pressure, generated in a separate 
steam boiler, is injected into the steam jacket beneath the still, so that the 
water in the still is brought to lively boiling, and each particle of the plant 
charge thoroughly and continually agitated. The quantity of the plant 
charge does not necessarily depend upon the size of the still. A ^somewhat 
loose charge contains sufficient interspaces to permit an unhindered pene- 
tration by the steam bubbles rising from the still bottom ; hence the charge 
can be higher than 4 in. If, in addition, the plant material does not agglu- 
tinate or lump while softening under the influence of heat, the charge may 
be considerably higher. However, complete exhaustion is not always 
assured ; in general, good results in the case of water distillation are obtained 
only if the charge is sufficiently low to permit the rising steam bubbles to 
overcome the weight of the plant charge. In other words, the steam should 
continually agitate the plant particles. In this case it is preferable to work 
without a perforated grid above the bottom of the retort. If, on the other 
hand, the charge is high, exercising a marked pressure upon the bottom, the 

18 Guenther and Garnier, "Bulgarian Rose Oil," Am. Perfumer 25 (1930), 621. 


insertion of a perforated grid is advisable. For certain types of plant ma- 
terials e.g., roses, orange blossoms, and ylang ylang flowers which can be 
kept floating in the boiling water by lively steam development, much deeper 
or spherical stills may be employed. Heating coils (instead of a steam 
jacket) should be avoided in this case because plant particles easily attach 
themselves to the coils and may give trouble. 

Very finely powdered material such as almond or apricot kernels 
has a tendency to "burn" in contact with the hot steam jacket; the water in 
the still should, therefore, be heated, not by indirect steam, but by direct 
steam, injected through a steam coil within the still. High, cylindrical 
stills arc better adapted to this purpose than wide, flat ones. In this case, 
the distillation water is collected separately, and not pumped back into the 
still during the process, because too much liquid would accumulate in the 
still by condensation of the injected live steam. 

A general rule which applies to all methods of distillation is that each 
charge should be completed on the same day. The quantity of plant ma- 
terial charged and the rate of distillation must be calculated accordingly. 
It should be kept in mind that the shorter the distillation, the less the forces 
causing hydrolysis, decomposition and rcsinificntion will come into action. 
The loss of essential oil arising from these forces may amount to several per 
cent, as calculated upon the oil. In the case of water distillation, it is 
not always possible, however, to shorten distillation to a one-day operation. 

Fig. 3.18 shows a still for water distillation, with automatic return of the 
distillation waters. 

Water and titeam Distillation. Let us now consider some practical as- 
pects of water and steam distillation, a method which in recent years has 
become quite popular among small producers using portable distillation 
equipment that can be moved from field to field, following the harvest. 
The smaller units are heated by direct fire, the larger ones by a steam jacket, 
a closed steam coil, or in rarer cases by open steam coils. When using direct 
fire, precaution must be taken to insure that only the bottom of the still, 
the section containing water below the grid which carries the plant charge, 
is heated. Otherwise, one of the major advantages of water and steam dis- 
tillation over water distillation, namely, freedom from the danger of over- 
heating the plant material, will be lost. As was stated previously, when this 
method of distillation is employed the plant charge itself is kept out of 
contact with boiling water. Hence, if the upper part of the still were ex- 
posed to direct fire, the plant material might be dangerously overheated. 
It is advisable, therefore, to use indirect steam as r, source of heat, but not 
direct fire. 

In this type of distillation, observing the precautions mentioned in the 
last paragraph, steam alone contacts the charge, the steam either being 



generated from, or passing through, water in the still. Thus overheating 
or drying of the charge is avoided because the temperature cannot rise above 
that of saturated steam at the pressure prevailing in the still (at atmospheric 
pressure never above 100). Water and steam distillation, therefore, repre- 
sents a typical case of distillation with saturated low pressure steam. For 


Water Outlet <*- r 

Steam Inl 

Water and Plant Material (f 


*, //y _^_ , /t , f ^ 



FIG. 3.18. Still for water distillation. 

this reason, the condensate contains fewer decomposition products than 
that obtained by direct steam distillation with live steam, and particularly 
with high pressure or superheated steam. 

Preparation of the plant material is much more important in this method 
of distillation than in water distillation. Since the steam contacts the 
material only by rising througn it, the plant charge must be so disposed 
that all parts of it are uniformly contacted, if high yields of oil are to be 


maintained. This requires that the charge be homogeneous as to size and, 
furthermore, that the average size of the individual pieces be controlled 
within rather narrow limits. If, for example, the material is finely ground, 
it will tend to pack and offer strong resistance to the passage of steam. 
This in turn may develop steam pressure beneath the charge until such pres- 
sure is sufficient to penetrate it. Such penetration, however, will take 
place at only a few places, releasing the pressure and permitting the steam 
to escape through only a few passages or channels sometimes called "rat 
holes." Obviously, under these circumstances most of the plant material is 
never contacted by the steam, and the recovery of oil is incomplete. If, 
on the other hand, a charge consists of, say, whole stalks, leaves and flowers, 
there obviously will be some fairly large passages through the charge which 
offer little or no resistance to the passage of steam. Steam will then escape 
through these and again permit m,ost of the charge to remain unaffected by it. 
Therefore, in the case of water and steam distillation, the plant material 
should not be too finely ground ; nor should it contain excessively long stalks 
or large roots or pieces of bark. Granulation usually gives the best results. 
Experience alone can determine the optimum size to which the material 
should be reduced, and this will vary from plant to plant. At any rate, the 
preparation of the charge for water and steam distillation must always be 
given most careful attention. 

Another problem to be considered in water and steam distillation arises 
from the fact that the charge is cold at the start, and that the first steam to 
enter it will condense, thus wetting the plant material. This wetting will 
continue until the entire charge reaches the boiling temperature of water at 
the operating pressure. With certain types of plant materials for ex- 
ample, leaves or ground seeds, bark, roots, etc.- excessive wetting may 
result in lumping or agglomeration of the charge and, therefore, in a sub- 
normal oil yield. Such wetting, again, may cause channeling of the steam. 
If a charge tends to agglomerate when wet, it is sometimes advisable to add 
dried twigs or short small pieces of stalk, or any other loose but absolutely 
neutral material, in limited quantities, so that the charge may be kept 
porous. To avoid continuation of wetting due to loss of heat by radiation 
from the walls of the still, the upper part of the retort in other words, 
the section housing the charge should be insulated. 

The rate of distillation in the case of water and steam distillation is not 
as important as in the case of water distillation. It affects only the rate of 
production but not always the quality or yield of oil. A lively pace of 
distillation recommends itself, however, in order to prevent excessive 
wetting of the plant charge and in order to increase the production rate. 
Regarding oil production per hour, water and steam distillation is less effi- 
cient than steam distillation; it approaches that of water distillation. 




Plant Charge 

1 o Condenser 

Compared with water distillation, water and steam distillation has the 
advantage in that it gives less rise to products of decomposition in the oil 
(hydrolysis of esters, polymerization, resinification, etc.) . As far as portable 
stills and small stationary posts are concerned, water and steam distillation 
is, in most cases, a better method than water distillation : it requires less fuel, 
shorter hours, and yields more oil even with a low rate of vaporization. If, 
however, a plant material for instance, roses or orange blossoms forms 
lumps under the influence of steam, the interspaces disappear and the steam 
can no longer penetrate the charge and reach every plant particle. In such 
cases, water distillation must be resorted to. 

The great disadvantage of water and steam distillation, which limits its 
adaptation, lies in the fact that, as a result of the low pressure of the rising 
steam, oils of high boiling range require large quantities of steam for com- 
plete vaporization hence long hours of distillation. In this process much 
steam condenses in the plant charge, which becomes increasingly wet, 
agglutinates, and will yield its oil only very slowly. 

As in the case of water distilla- 
tion, in water and steam distillation 
the condenser can be installed at 
such a height that the distillation 
water flows automatically and con- 
tinuously back into the still. Or the 
distillation water may be pumped 
back, or injected into the retort. 

After completion of a charge, the 
water beneath the perforated grid is 
discarded, and replaced with fresh 
water. It is not advisable to em- 
ploy the same water for the next 
harge because some steam always 
condenses within the plant charge, 
and water-soluble extractive matter 
from the plant charge accumulates 
in the water beneath the grid. The 
repeated use and boiling of the same 
water may cause the extractive plant matter to decompose, and to form 
volatile products of disagreeable odor, which are liable to impart an objec- 
tionable by-note to the volatile oil. 

Summarizing, it can be said that water and steam distillation must be 
carried out by observing the following principles: uniform size of the plant 
particles and sufficiently large interspaces for the rising steam ; uniform dis- 
tribution of the plant material in the retort, so that the charge is penetrated 


FIG. 3.19. 

Still for water and steam 



evenly and completely by steam. Although the method of direct steam 
distillation serves for a variety of plant materials, water and steam distilla- 
tion is suitable only for certain types. It is especially adapted to field 
distillation in small or medium sized stills. 

Water and steam distillation can also be carried out under reduced or 
increased pressure. Indeed, in some cases, reduced pressure gives excellent 

Fig. 3.19 shows a retort for water and steam distillation. 

t-- "vrMfc . v> j^rjLjO-' 

Courtesy of Mr. F. Gutkind, London, England. 

PLATE 4. Field distillation of rosemary in Tunis. The stills are directly fired. 
The plant material is transported by camels to the distillation post. 

Steam Distillation. Live steam, usually of a pressure higher than at- 
mospheric, is generated in a separate steam boiler, and injected into the 
plant charge within the retort. This type of distillation is referred to as 
direct steam distillation, or distillation with live steam, or dry steam 
distillation. Most aromatic plants are distilled today with direct live steam 
at atmospheric pressure. 

The application of steam distillation is subject to exactly the same reser- 
vations mentioned in the discussion of water and steam distillation, plus 
one additional factor. When using steam distillation, it is always possible, 
after the initial period during which the charge in the retort is warming up 
and condensation taking p.lace, that the steam may be slightly superheated. 
Indeed, in some cases the steam may be purposely superheated, as already 
mentioned, in order to improve the oil to water ratio. In expanding from 


the much higher boiler pressure to the lower pressure prevailing within the 
retort, the steam tends to become superheated. Two factors then assume 
importance. First, the temperature of the charge will no longer be main- 
tained at the boiling point of water, under the operating pressure, but will 
rise to the temperature of the superheated steam. The operator, therefore, 
must guard carefully against overheating. Second, superheated steam has a 
tendency to dry out the charge and reduce the rate of recovery of the es- 
sential oil. As was pointed out above, a good part of the oil is vaporized 
only after diffusing, as an aqueous solution, through the cell membranes to 
the outside of the plant particles. This diffusion, however, becomes pos- 
sible only by the presence of a certain amount of hot water, and may be 
stopped altogether, or seriously slowed down, when the charge is completely 
dried. If, therefore, in the case of direct steam distillation, the flow of oil 
stops prematurely, it may be necessary to continue distillation with satu- 
rated (wet) steam for a time, until hydrodiffusion is re-established. After 
that slightly superheated steam may again be employed. 

In general, it can be said that direct steam distillation excels water dis- 
tillation, as well as water and steam distillation in regard to cost, rate of 
distillation, and capacity of production. As far as the condition of the 
plant material and the method of charging are concerned, the same principles 
apply here as to water and steam distillation. Special attention must be 
paid to the quality of the live steam. The higher the pressure of the steam, 
the higher is the temperature at which it enters the still ; but in this respect 
the moisture content of the steam plays an important role. Saturated & earn 
usually carries some water in the form of minute droplets, which are con- 
densed by the expanding steam. Hence, the effect of superheating becomes 
noticeable only if saturated (but dry) steam, of markedly high pressure, is 
used. The higher the pressure of the steam in the steam boiler, the drier 
the plant material will remain during distillation. Only the portions of the 
charge touching the still walls will then become moist through condensation, 
despite insulation of the still against emanation of heat. In order to limit 
such loss of heat, and consequent excessive lowering of the temperature, 
the high-pressure steam, before entering the still, is sent through a water 
separator, and partly dried. In this connection, it should also be kept in 
mind that the different systems of steam boilers generate live steam, con- 
taining more or less moisture. In cases of prolonged distillation, consider- 
able quantities of steam are condensed in the plant charge, and water ac- 
cumulates on the bottom of the still. This may give trouble by wetting the 
lower part of the plant charge. Such condensed water must be drawn off, 
from time to time, through a stopcock in the still bottom. 

Since high-pressure steam causes considerable decomposition, distilla- 
tion is best started with steam of low pressure, followed by steam of higher 


pressure toward the end of the operation, when the oil content of the charge 
has decreased considerably, and when chiefly the high boiling constituents 
of the essential oil remain in the retort. No general rule can be laid down 
in this respect, as every type of plant material requires a different and specific 
method of preparation and also of distillation. 

End of Distillation. As the distillation proceeds, and as the oil content 
of the charge decreases correspondingly, the ratio of water to oil in the con- 
densate will increase, because the steam can no longer contact the oil in the 
charge efficiently, regardless of the rate of distillation, and also because the 
remaining constituents are mostly high boiling. The operator must then 
decide at what point it is no longer economical to continue the distillation. 
Several criteria can be applied here. From a knowledge of the size of the 
charge and the yield to be expected, and from experience or trial distillations 
in a pilot still, it can quickly be determined whether or not the charge has 
been nearly exhausted. If yield data on the particular material charged 
are not available, it usually will suffice to take a small sample of the con- 
densate directly into a test tube or glass cylinder and estimate from this the 
rate at which oil is being distilled at any particular time. Then, knowing 
the amount of oil already distilled, and calculating the amount that will be 
distilled in any additional period of time, it can be decided whether distilla- 
tion should be continued for that period, or whether it would be more eco- 
nomical to stop and begin a fresh charge. The value of the product also 
enters into consideration, since a very valuable oil can be run profitably to 
a much larger water to oil ratio than can a less valuable oil. Certain oils 
e.g., vetiver or angelica root oil contain their most valuable constituents 
in the last runs (highest boiling fractions), and in these cases distillation must 
be prolonged for hours even though almost no oil seems to distill over toward 
the end of the operation. Otherwise valuable, high boiling constituents 
will be lacking in the oil. This rule, by the way, applies to all types of 

It should also be kept in mind that the oil to water ratio measured at 
any time during distillation will always be higher than during any succeed- 
ing period, since this ratio decreases as the distillation continues. Experi- 
ence with the distillation of any particular plant material will enable the 
operator to evaluate these matters properly, so as to obtain a maximum 
yield, a maximum rate, and a high quality of oil. 

Treatment of the Volatile Oil. The handling of the condensed oil is 
worthy of brief comment since its quality may deteriorate, particularly if 
the oil must be stored for some time. Just as the condensed water (distilla- 
tion water) is always saturated with oil, so the condensed oil will always be 
saturated with water. There remains also the probability of slow reaction 
between the oil and water, unless the latter is almost completely removed. 


The oil can be brightened (cleared of cloudy appearance) by filtering through 
kieselguhr or magnesium carbonate on filter paper. . This procedure removes 
all small droplets of water which cause the cloudiness, but it does not com- 
pletely dry the oil. Larger quantities of oil may be filtered through me- 
chanical filters, filter presses, or run through high-speed centrifuges. For 
further details see the section in the Appendix on "The Storage of Essential 

Treatment of the Distillation Water. The distillation water flowing off 
the oil separator (Florentine flask) contains some of the volatile oil in solu- 
tion or suspension, the quantity depending upon the solubility and specific 
gravity of the various oil constituents. Considering that the distillate pre- 
sents a mixture of condensed steam and oil vapors, it is evident that the 
water phase of the distillate actually represents an aqueous solution of oil, 
completely saturated at the prevailing temperature. Those oil constituents 
which are somewhat soluble in water will be partly dissolved in the distilla- 
tion water, and the dissolved portion of this oil will be different in composi- 
tion from that of the oil separated in the Florentine flask. The latter is 
usually called main or direct oil, the former water oil. The water-soluble 
constituents consist mostly of oxygenated compounds, and since these com- 
pounds possess a higher specific gravity than nonoxygenated compounds 
(terpenes, sesquiterpenes, etc.), the water oil usually has a higher specific 
gravity than the main oil. This difference, however, is not always pro- 
nounced, because the distillation water contains not only oil in actual solu- 
tion, but also in suspended (minute droplets) and emulsified form. A more 
or less milky appearance of the distillation water thus indicates the presence 
of oil. 

Such distillation water cannot be discarded, but must be submitted to 
further treatment to prevent loss of oil. In the case of water distillation or 
water and steam distillation, it may be automatically returned into the re- 
tort during distillation. For this purpose the Florentine flask must be 
installed at a sufficient height above the still so that the flow from the 
flask overcomes the pressure within the still. In the case of steam distilla- 
tion (with live steam from a separate steam boiler) the distillation water 
should not be returned into the retort, as too much liquid would condense 
and accumulate within it and wet the plant charge. The distillation water 
therefore, is pumped or injected into a separate still for redistillation. The 
process of recovering the oil from the water by redistillation is commonly 
called cohobation, the stills serving for this purpose being known as cohoba- 
tion stills. In its original and stricter sense, the term "cohobation" implies 
that the distillation water is used over and over for the distillation of a new 
plant charge (in the case of water distillation or water and steam distillation), 
but today cohobation simply means redistillation of the distillation waters. 


The distillation waters are redistilled most efficiently in round stills 
provided with a steam jacket or a closed steam coil. Indirect heating is 
preferable, because the injection of live steam into the retort would cause 
too much water to accumulate within the retort, and hinder the vaporiza- 
tion of the oil from the water. In the case of many distillation waters only 
10 to 15 per cent need be distilled off to recover most of the oil dissolved or 
suspended therein. The residual water may be discarded. Occasionally, 
however, it is necessary to distill off more than half of the quantity of water ; 
in such case, a considerable portion of the oil distilled over will again be dis- 
solved in the distillation water. To shorten the cohobation and increase 
the quantity of oil in the condensate, the water in the cohobation still is 
saturated with common salt (NaCl). This decreases the solubility of the 
volatile oil in water: the oil distills over more quickly, and with a smaller 
quantity of water. This procedure is recommended particularly where the 
distillation water contains slightly water-soluble constituents of high boiling 
point, which cannot be recovered by mere steam distillation. 

The separation of oil and water by cohobation is based upon the simple 
principle that a mixture of oil vapors and steam possesses a slightly lower 
boiling point than pure water vapors (steam), and that the vapor mixture 
arising contains more oil than the liquid phase. By a reduction of the speed 
of cohobation, the oil content of the distillate may be increased because the 
rising steam will be more thoroughly saturated with oil vapors. 

The following figures cited by Folsch 17 give an idea of the quantities of 
volatile oils which can be obtained by the cohobation of various distillation 
waters : 

Quantity of Water Oil Recovered 

from 1,000 kg. of Distillation 
Plant Material Water (grams) 

Chamomile Flowers 100-120 

Coriander Seed 625-650 

Dill Seed 360-450 

Fennel Seed . . 175-200 

Lavender Flowers. . 150-200 

Peppermint Herb. 400-500 

Sage Herb . . 300 

Tansy Herb 540 

Another method of recovering the oil dissolved or suspended in the dis- 
tillation water consists in saturating the latter first with salt and then ex- 
tracting the solution with volatile solvents e.g., highly purified petroleum 
ether or benzene. This is usually done twice. The drawn off and united 
solvent solutions are then concentrated in a still by driving off the solvent, 

17 "Die Fabrikation und Verarbeitung von atherischen Olen," Wien und Leipzig (1930), 


first at atmospheric pressure, and later in vacuo, until every trace of solvent 
is eliminated from the oil. 

Any distillation of aromatic plants, unless conducted at fairly low tem- 
peratures, gives rise to products of decomposition in the nonvolatile plant 
constituents. These products (methyl alcohol, formaldehyde, acetaldehyde, 
acetone, low fatty acids, nitrogenous compounds, phenols, etc.) are carried 
into the condensate and present objectionable impurities. Because of their 
water solubility, they dissolve mainly in the distillation water, since the 
quantity of water by far exceeds that of oil. Because of the presence of such 
decomposition products, the crude water oil obtained by cohobation or 
extraction will in most cases be of dark color, often of disagreeable odor. 
It should not be combined with the main oil, as it would spoil the odor and 
flavor of the latter. It is, therefore, advisable to rectify the crude water 
oil by fractionation in a good vacuum still. 

In many cases the great water solubility of the aforementioned decom- 
position products serves for the purification of volatile oils : when rectifying 
(redistilling) an oil by hydrodistillation, the distillation water is then simply 

Disposal of the Spent Plant Material. The disposal of the spent plant 
material, which represents a rather large bulk, frequently offers an annoying 
problem. One very economical method of disposal consists in using it as 
fuel after air drying, of course, either in the sun or near the still in the case 
of direct fire stills, or near the boiler when a separate steam generator is used. 
Since the spent material has a rather low fuel value per unit volume, con- 
sideration must be given to the construction of a special fuel box. In 
many cases the spent material may be used effectively as fertilizer. Certain 
spent plants make an excellent cattle feed ; this is particularly true of seeds 
which contain a high percentage of protein and fatty oil. The drying is 
done in dehydrating apparatus or by air drying on shelves. When sweet- 
ened with molasses, some spent grasses, such as lemongrass, seem to be 
relished by cattle. 

Trial Distillation. No discussion of distillation as used in the essential 
oil industry would be complete without some consideration of the interpre- 
tation to be placed upon the results of laboratory distillations, or, as they 
are frequently called, trial distillations. Since the oil content of plant ma- 
terial to be distilled fluctuates rather widely with such variables as geo- 
graphical origin, growing conditions, ambient temperature, rainfall, period 
of harvest, moisture content, etc., it is not usually possible to state any 
values for the oil content other than by upper and lower limits (which in 
some cases may be quite widely separated). As already pointed out, han- 
dling of the plant material after harvesting, and prior to distillation, also has 
a marked effect on the oil content. As knowledge of the efficiency with 


which a large scale distillation is being conducted can be obtained only by 
comparison of the actual yield with the possible yield, it becomes quite 
important that the latter value be known with some accuracy. The only 
means of determining this value is to conduct a laboratory distillation using 
a sample of the plant material to be distilled in the larger scale operation. 

The aim of any commercial distillation is, of course, to recover as large 
a percentage of the valuable oils in as high a state of purity as possible. 
Only in the laboratory, on a small scale, and under carefully controlled con- 
ditions, can both of these conditions be met. Therefore, the results of such 
laboratory distillation may be considered as a standard which the large- 
scale operation should approach as closely as practically possible. 

There are two ways of carrying out such trial distillations : (a) on a very 
small scale in a glass flask, and (b) on a larger scale in a pilot still. 

(a) Numerous methods of assaying the contents of essential oil in plant 
materials have been suggested. The literature offers many modifications 
of these methods, all of which aim at a quantitative yield of oil. The best 
and most commonly used method is that of Clevenger, which has found 
official recognition in "Methods of Analysis/' published by the Association 
of Official Agricultural Chemists, Fifth Edition, 1940. For details of Cle- 
venger's method see below, Chapter 4, on "The Examination and An- 
alysis of Essential Oils, Synthetics and Isolates." This method permits 
assaying quantitatively the content of essential oil in a small amount (50 
to 500 g.) of plant material. Although the amount of oil thus obtained is 
not sufficient to carry out a complete analysis, conclusions regarding its 
odor and flavor characteristics can be drawn from the small sample. Occa- 
sionally, the oil will have to be set aside for several days, until the slightly 
"burnt" or "still" odor of the freshly distilled oil has disappeared. 

(6) A much more satisfactory method consists in distilling a sample of 
20 to 50 Ib. of aromatic plant material in a regular "pilot" still. Such a 
still, made of tin-lined copper, should be constructed so as to embody all 
the characteristics of large stills. It should allow for water distillation, 
water and steam distillation, and direct steam distillation. It will thus be 
possible to find for each new plant material the most appropriate method of 
distillation, to study, as well as possible, the rate of distillation and the con- 
sumption of steam (by measuring the quantity of distillation water*), and 
to determine the maximum yield of oil. Interesting observations regarding 
the effects of hydrodiffusion can be made. In the case of direct steam distil- 
lation the use of high-pressure or superheated steam may be studied. The 
quantity of oil recovered will be sufficiently large to examine the oil analyti- 
cally, even to fractionate it. The pilot still should be provided with several 

* This will be only approximately correct, since heat losses from the distillation 
system have not been considered. 



trays, in order to find out the most opportune way of charging, if seed ma- 
terials are to be processed. A small crusher and hay cutter will permit try- 
ing out the effects of comminuting the plant material according to different 
sizes. Needless to say, the pilot still should be well insulated in other 
words it should resemble large stills in every possible way except size. 

For all-around operation the pilot still should also be equipped for auto- 
matic return of the distillation waters into the still, in the case of water 
distillation or water and steam distillation, if the return (cohobation) of 
these waters into the still during operation seems desirable. In the case of 
direct steam distillation, the distillation water or a small measured part of 

j) Temperature Gauge 




FIG. 3.20. Sketch of an experimental still. 

it is saturated with ordinary salt, and three times extracted with low boiling 
petroleum ether. The drawn off and united petroleum ether extracts are 
then carefully evaporated on a hot water bath, and the residue dried in a 
desiccator to constant weight. From this small quantity the oil content of 
the total distillation waters can be calculated. Obviously, the extraction of 
only a part of the distillation waters gives an exact result only where the 
total distillation waters, after completion of the distillation, have been 
bulked in a tank. The distillation water should always be processed right 
after distillation of the plant material, because when exposed to the air for 
some time it loses oil by evaporation. While a small part of the distillation 
water is extracted experimentally with a solvent, another part should be 
steam distilled (cohobated). If cohobation yields no oil, the distillation 
water will have to be extracted with solvents. 



Figs. 3.20 and 3.21 show the construction of pilot stills which may have 
a capacity of about 50 gal. 

Steam Consumption in Plant Distillation. In the distillation of aromatic 
plants the distillate (condensed water and oil) usually contains much more 
water than if the isolated oil itself had been hydrodistilled. 

The following table indicates the average oil content, by weight percent- 
age, in the distillates of completed operations as established by von Rechen- 
berg, 18 based upon years of experience with industrial distillation of aromatic 

Distillation of Plant Material; Average Content of Volatile Oil in the Distillate 

Plant Material 

% Oil 

Ajowan Seed . .... 0.77 

Angelica Seed. . . .... 0.19 

Angelica Root, Fresh . ... 0.03 

Anise Seed . 0.81 lo 1.16 

Arnica Flowers . . . 0.001 

Arnica Hoot, Dry . 0.06 

Bay Leaves . . 0.75 to 0.77 

Calamus Root, Dry. . . . 0.23 to 0.24 

Calamus Root, Fresh. ... ... 0.12 

Caraway Seed 2.22 to 3.04 

Cedar Wood . . . . 0.97 to 1.41 

Celery Seed.. . .. . 0.17 

Chamomile Flowers, Dry. . . 0.004 to 0.007 

Cinnamon Ceylon 0.31 to 0.34 

(loves . . . 0.60 to 0.86 

Clove Stems. . . 1.03 to 1.52 

Coriander Seed . . . 0.56 to 0.57 

Costus Root, Dry. ... 0.01 

Cubebs 1.2 

Cypress 0.12 to 0.2 

Elecampane Root ... 0.05 

Fennel Seed 1.42 to 2.08 

Galangal Root 0.05 to 0.08 

Ginger Rool 0.28 

Juniper Berries . . 0.20 

Lovage Root, Dry . . 0.05 

Lovage Root, Fresh 0.02 

Lovage Herb, Fresh 0.02 

Patchouli Leaves 0.12 to 0.13 

Peppermint Herb, Fresh . . .0.11 

Pimenta Berries. . ... .0.18 

Sandalwood, East Indian. ... . . 0.05 to 0.16 

Sandalwood, West Indian . .. 0.23 to 0.34 

Savin ... 0.25 to 0.31 

Vetiver Root . . 0.015 to 0.02 

18 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig (1910), 362. 



FIG. 3.21. Sketch of an experimental still with automatic cohobation. 

Let us now compare these data with those expressing the composition 
of the condensate resulting from hydrodistillation of some of the pure 
chemical compounds which occur in volatile oils. 

Hydrodistillation Content in the 

of Distillate (%) 

Styrene 57.0 

p-Cymene 45.7 

Pinene 55.6 

Limonene 40.0 

Dipentem* 40.0 

Linalool 18.2 

Menthol 12.0 

Carvone 9.7 

Anethole. . 7.1 

Cinnamaldehyde 3.0 

Eugenol 1.7 

Santalol 0.5 

Occurs in 
Cinnamon oil 
Ajowan oil 
A jo wan oil 
Caraway oil 
Ajowan oil 
Coriander oil 
Peppermint oil 
Caraway oil 

Anise, fennel and star anise oil 
Cinnamon and cassia oil 
Clove, clove stem, pimenta, bay 

and cinnamon oil 
East Indian sandalwood oil 

What are the causes of the marked increase in steam consumption during 
distillation of plant material, as compared with steam consumption during 
hydrodistillation of essential oils per sef Von Re^henberg 19 demonstrated 
that, in the case of caraway seed distillation, the condensate contains only 

19 Ibid., 366. 


2.22 to 3.04 per cent oil, whereas in the case of caraway oil distillation the 
condensate contains 8.80 to 10.11 per cent of oil. This obviously implies a 
much greater consumption of steam, in the first case, for the same quantity 
of oil, and longer hours of distillation. 

The paucity of oil in the distillation of plant material, according to the 
same author, is caused by several factors : 

1. Many aromatic plants contain a quantity of oil insufficient to saturate 
the relatively large quantities of steam blowing rapidly through the plant 
charge. On the other hand, it is not advisable to reduce the speed (rate) 
of distillation below a certain limit. A high steam velocity causes pressure 
differentials within the still, which prevent the steam from stagnating in the 
more densely packed parts of the plant filling. For this reason, and in 
order to increase the efficiency of a still, the operator is always tempted to 
inject into the still much more steam than is actually required. This 
results in a large volume of distillation water. 

Example: Let us suppose that a charge of 2,000 kg. of plant 
material can be exhausted in 11 hours, if we inject 250 kg./hr. 
steam (250 kg. distillation water in 1 hour). If, instead, we in- 
ject twice the amount of steam, i.e., 500 kg./hr., the length of 
distillation will be shortened at best by one-third, and in most 
cases only by one-fourth; but not by one-half, as might be 

2. In the course of distillation the oil content of the plant charge de- 
creases gradually and the vaporization of oil is not stopped abruptly toward 
the end of the operation. This does not even take place in hydrodistillation 
of volatile oils per se, and much less with plant material. Plainly, such a 
prolongation of the distillation greatly increases the steam consumption and 
depends also upon the individual operator. 

3. While retained in the plant material, the volatile oil may be subjected 
also to forces of adhesion ; this seems true even if small quantities of oil are 
distributed over large surfaces of comminuted plant particles. Experi- 
ments to this effect were undertaken by Rodewald. 20 

4. The volatile oil is enclosed within the plant tissue and cut off from 
direct contact with steam by several layers of membrane, often very tough. 
For this reason most plant materials must be comminuted prior to distilla- 
tion. Where steam distillation is practiced, this process of comminuting 
(grinding, pounding, milling, crushing, rasping) should not be carried too 
far (certainly not to the point of reducing the material to the size of flour 
particles), because the interspaces within the plant charge would then be- 
come too small. The rising steam must have sufficient space to penetrate 
all parts of the charge uniformly. Very small interspaces necessitate a slow, 

20 Z. physik. Chem. 24 (1897), 193. 


ineffective distillation, because any increase in pressure would cause the 
steam to break channels ("rat holes") through the plant charge, or to hurl 
parts into the gooseneck and condenser. In other words, too finely powd- 
ered material is not penetrated evenly by steam and cannot be completely 
exhausted by steam distillation. 

If, on the other hand, the plant material is not powdered, but granulated, 
only a portion of the oil is freed, and another portion remains enclosed within 
the oil glands in the plant tissue. When crushing plant material, such as 
seed, a portion of the freed volatile oil will be covered again by crushed plant 
particles. The distillation of excessively crushed seed material, if not 
properly conducted, may, therefore, require longer hours than that of torn 
or slightly milled seed, provided the quantity of injected steam is the same. 

If the plant material is distilled in uncomminuted condition as with 
herbs and leaves, and most flowers the oil remains enclosed within the 
plant tissue. Hacking with an axe or machete or cutting in a hay cutter 
offers an advantage only in that the material can be packed into the still 
more uniformly ; the steam then penetrates the charge more evenly, but very 
few oil glands will actually be broken up. Since the steam can vaporize 
only those volatile substances which it touches directly, and will not affect 
the oil enclosed within the plant tissue, the oil must first be dissolved by hot 
(liquid) water and carried, by diffusion, through the swollen cell walls to- 
ward the outside. Hydrodiffusion, however, requires much more time than 
vaporization, which takes place almost immediately, because all the en- 
closed volatile oil must be brought to the surface, and that is a slow process. 
This fact is primarily responsible for the paucity of oil in the condorisate, 
and for the relatively long duration of distillation in the case of uncom- 
minuted leaves and herbs possessing a tough fiber. 

5. If the plant material is comminuted prior to distillation, very high 
boiling or practically nonvolatile substances, such as resins, paraffins, 
waxes, fatty oils (contained in other cells or glands), mix with and dissolve 
in the freed volatile oil, thereby substantially lowering its vapor pressure, 
and reducing its rate of vaporization. This occurs particularly in the case of 
seeds, most of which contain large quantities of fatty oils. The Agricultural 
Experiment Station of Mockern, near Leipzig, Germany, reported the fol- 
lowing content of fat and fatty oil (ether extract) in seeds from which the 
volatile oil had first been removed by steam distillation : 

Seeds Fatty Oil (%) 

Ajowan 33.20 

Anise 18.59 

Caraway 16.06 

Celery 31.32 

Coriander 26.40 

Fennel 16.71 


Assuming that air-dried caraway seed, such as is used for distillation, 
contains about 15 per cent moisture and 5.5 per cent volatile oil, we arrive 
at a ratio of 5.5 per cent volatile oil to 12.8 per cent of fatty oil in the seed. 
For practical distillation, this implies that 5.5 parts of volatile oil must be 
vaporized from 12.8 parts of fatty, nonvolatile oil. In other words, it is 
necessary to distill a mixture of fatty oil and volatile oil, which holds 30 per 
cent of volatile substances in solution. Assuming a content of 5.0 per cent 
volatile oil in fennel seed, 3.0 per cent of volatile oil in anise seed, 3.5 per cent 
in ajowan seed, 2.5 per cent in celery seed and 1.0 per cent in coriander seed, 
we find that we would have to distill : 

Ajowan oil mixture containing 11.5% volatile oil* 
Anise oil mixture containing 16.0% volatile oil 
Caraway oil mixture containing 30.0% volatile oil 
Celery oil mixture containing 9.7% volatile oil 
Coriander oil mixture containing 4.2% volatile oil 
Fennel oil mixture containing 27% volatile oil 

Such relatively large quantities of fatty, nonvolatile oils are well capable 
of reducing the vapor pressure, and thereby the rate of vaporization of the 
volatile oils dissolved in these fatty oils. 

Other reasons aside, it is thus practically impossible, when distilling seed 
with steam or boiling water, to saturate the steam completely with oil 
vapors, even when packing the plant charge very high in the still. The oil 
vapor phase in this mixture will always remain unsaturated ; the more the 
content of fat in the seed exceeds thut of volatile oil, the less the steam will 
be saturated with volatile oil vapors. This theoretical consideration con- 
firms practical experience in the case of seed distillation. In actual practice, 
therefore, distillation of seed material can seldom if ever be completed, be- 
cause the fatty oil tends to retain small quantities of volatile oil. It be- 
comes necessary, therefore, to halt distillation, since the small recovery of 
oil no longer warrants the increasing consumption of steam and labor. 

6. The steam consumption is influenced further by the moisture content 
of the plant material, particularly in the case of herbs, grasses and roots, 
which are processed either in the fresh succulent, or scmidry, or dry, condi- 
tion. When distilling peppermint herb with live steam, for instance, the 
following quantities of steam will be consumed, the steam consumption being 
measured by the quantity of distillation water in the condensate : 

Fresh herb requires 250 to 350 kg. of steam per kilogram of oil. 
Semidried herb requires 60 to 80 kg. of steam per kilogram 

of oil. 

Air-dried herb requires 30 to 40 kg. of steam per kilogram of oil. 
* In all cases a 15% moisture content of the seed is assumed. 


These figures, cited by Folsch, 21 are evidently relative, as actual steam 
consumption depends upon the type of the still, the quality of the steam, 
the way of packing, and the experience of the operator. 

Because of its high moisture content, fresh peppermint herb, when dis- 
tilled, has a tendency to lump (agglutinate) and to prevent a uniform pene- 
tration by the steam. The volatile oil is, therefore, released from the fresh 
herb only very slowly. Taking the above figures of steam consumption as 
a basis, the steam/oil vapor mixture (in other words, the condensate) will 
contain the following quantities of volatile oil : 

Fresh Herb 0.3 to 0.4% peppermint oil 

Semidried Herb 1.2 to 1.6% peppermint oil 

Air-dried Herb 2.5 to 3.0% peppermint oil 

The oil content in the condensate is not uniform from the beginning to 
the end of distillation, but amounts in the beginning to a multiple of the 
average oil content. In the case of air-dried peppermint herb, the con- 
densate contains in the beginning about 8 per cent of oil, which decreases 
gradually toward the end until it amounts to only 0.004 per cent. For prac- 
tical reasons distillation should then be stopped. As mentioned previously, 
certain plants contain volatile oils, the most valuable parts of which are 
very high boiling. When applying saturated steam of atmospheric pressure 
only, distillation must then be continued for very long periods, although 
only small quantities of oil are recovered toward the end. If this is not done 
the high boiling constituents are lacking in the oil, and the oil is of inferior 
quality. In such cases it will be advantageous to speed up and complete 
the operation by injecting slightly superheated steam toward the end. 

Rate of Distillation.- According to Folsch, 22 the ratio between quantity 
of distillation (condensed) water and time (in other words, the quantity of 
water distilled over per hour) may be designated as rate (force or speed) 
of distillation. It must be regulated according to the diameter of the still, 
and the size of the interspaces within the plant charge (degree of comminu- 
tion). If the velocity of the rising steam is too low, the steam will stagnate 
in the denser portions of the charge, and complete exhaustion by distillation 
will be impossible. If, on the other hand, the velocity is too high, the steam 
may break through the charge, form steam channels ("rat holes") and even 
hurl plant particles into the condenser, partly clogging it. By collecting 
the distillation water running off the condenser from time to time, and over 
a period of some minutes, and then weighing it, the rate of distillation can be 
controlled. For practical purposes the volatile oil may be ignored. The 

21 "Die Fabrikation und Verarbeitung von atherischen Olen," Wien und Leipzig 
(1930), 40. 

22 /bid., 62. 


quantity of distillation water collected during these few minutes is calcu- 
lated in terms of kilogram/hours per square meter. (See example below.) 
This figure is then compared with the optimum rate of distillation, as es- 
tablished by trial distillation or by experience with the plant material in 
question (and taking into consideration its degree of comminution). The 
steam velocity in the actual operation may be regulated accordingly. 

For example, if we obtain in one minute 8 kg. of distillation water, and 
if the smallest area covered by the charge on the perforated grid in a cylin- 
drical still is 1.2 sq. m., the rate of distillation will be 

8 X 60 AM . n 
1 = 400 kg./hr. per sq. m. 
i .z 

Once the average oil content of the mixed vapors (steam plus oil vapors) 
has been established for a certain type of plant material and a certain de- 
gree of comminution, and once the most favorable rate of distillation is 
known, the amount of steam necessary for complete exhaustion of a plant 
charge can be calculated, and the steam supply adjusted accordingly. By 
weighing the quantity of distillation water from time to time, by converting 
the figures to the total length of distillation and by relating this to the quan- 
tity of oil expected, the operation may thus be regulated according to opti- 
mum conditions. Let us suppose, for example, that 1,000 kg. of coriander 
seed must be distilled, and that the seed, according to assay, contains 0.8 
per cent of oil, in other words that the 1,000 kg. of coriander seed contain 8 
kg. of oil. We know from experience or from trial distillations that the 
average oil content of the vapor mixture (condensate) in the case of coriander 
seed distillation is 0.5 per cent. Therefore, 1,600 kg. of steam are required 
to distill over 8 kg. of coriander seed oil. If we work with a distillation 
rate of 200 kg./hr., i.e., 200 kg. distillation water per hour, the charge should 
be exhausted in 8 hr. In order to shorten the time of distillation, the rate 
of distillation must be increased. However, in this case attention must be 
paid to the fact that, on increasing the speed of distillation, the average oil 
content of the vapor mixture decreases to a certain extent, because the 
quicker the steam penetrates the plant charge the less it has occasion to 
become saturated with oil vapors. In other words, much more steam will 
be consumed than is calculated theoretically. 

Pressure Differential Within the Still. The velocity of steam flow is 
caused by differences in pressure. In the case of plant distillation with 
live steam, which in the boiler is usually at a pressure above atmospheric, 
the plant charge in the retort prevents the injected steam from expanding 
immediately and completely. For this reason, the steam pressure cannot 
fall immediately to the level of the atmospheric pressure. Thus, there 
arises a certain excess pressure beneath the charge in the retort; but a grad- 


ual equalization with the atmospheric pressure takes place toward the top 
of the still. The degree of this excess pressure is a function of the force 
(speed) of distillation and of the interspaces within the plant charge. Ac- 
cording to the height of the charge or the number of layers, this excess pres- 
sure can be increased by 0.3 atmospheres, and, in some cases, even more. 
But if the pressure exceeds a certain limit (which depends upon the type and 
height of the plant charge), the steam forms fine, often scarcely visible 
channels through a powdered charge, whereas coarser masses are torn apart, 
or even hurled into the gooseneck of the still. An excess pressure ("back 
pressure") within the retort may be caused also by a gooseneck or condenser 
pipes too narrow for the volume of steam injected into the still or by sharp 
bends in the pipes. 

Irregular heating of the boiler and variations in the steam consumption 
(such as are occasioned by the turning on and turning off of neighboring 
stills) may cause the pressure in a steam generator to undergo continuous 
fluctuations. High-pressure steam has a tendency to blow into a still 
somewhat jerkily, giving rise to pressure variations even within the retort. 
Such fluctuations, however, are by no means harmful ; on the contrary, they 
may exert a beneficial influence, as far as the yield of oil is concerned, by 
Forcing the injected steam to loosen and penetrate the more densely packed 
portions of the plant charge, where the steam would otherwise stagnate. 

Pressure Differential Inside and Outside of the Oil Glands. As it rises 
through the plant charge, the steam at first vaporizes all the freed volatile 
31! which by comminution of the plant material is within reach of the parsing 
steam. Saturated steam (not superheated!) will at the same time condense 
i certain quantity of water within the retort. Consequently, the tempera- 
ture of high pressure steam will be reduced to that of saturated steam, in 
Dther words, to the boiling point of the water/oil mixture. It must be re- 
membered that this boiling point is slightly lower than that of the saturated 
steam. As the volatile oil vaporizes from the plant material, the tempera- 
ture of the steam rises again to that of pure saturated steam, at the pressure 
prevailing in the charge. If the plant charge is somewhat tightly packed, 
the temperature of the steam will show a certain range from the bottom to 
the top of the charge. This differential in temperature depends upon the 
Force of distillation and the drop in the steam pressure from the lower to the 
upper section of the retort; in other words, the lowest part of the charge will 
tiave the highest, and the upper part the lowest, temperature. Gradually 
the temperature of the steam equalizes itself throughout the charge and, 
despite poor heat conduction, will prevail, even inside of all plant particles. 
ALS has been said, the boiling point of a water/oil mixture is somewhat lower 
than that of steam alone, the total vapor pressure a little higher. Since the 
temperature inside and outside of the plant particles has become equalized, 


a certain excess pressure will develop within those oil glands which still 
contain volatile oil and water enclosed. This pressure differential inside and 
outside of the oil glands probably has some influence upon the vaporization 
of the volatile oil through the cell walls. A sufficiently large pressure differ- 
ential may well cause some cell membranes to burst (provided they are not 
too thick and strong) or at least to expand the cell walls, to enlarge the 
pores and to loosen agglomerated particles of the charge, thus opening new 
passages for the steam. The more the pressure differential is reduced, the 
more it loses its significance as a loosening agent ; but it remains important 
for the isolation of oil, in so far as it supports the forces of hydrodiffusion. 
The pressure differential inside and outside of the oil glands is more effec- 
tive when first heating the retort and toward the end of distillation, provided 
temperature and pressure fluctuations actually occur inside of the still. A 
pressure differential, however, can be created only if water is present in 
liquid form, or by partial condensation of steam when first heating the 
retort : the water thus formed will penetrate the plant tissue and seep also 
into the oil glands, (von Rechenberg). 

In the hydrodistillation of plant material at reduced pressure, the pres- 
sure differential inside and outside of the oil glands exerts itself to a marked 
degree only with low boiling substances. In the case of distillation above 
atmospheric pressure, however, the pressure differential assumes consider- 
able importance. 

Effect of Moisture and Heat upon the Plant Tissue. Any plant material 
serving for distillation contains a certain quantity of moisture, even air- 
dried material retaining 10 to 20 per cent of water. If saturated steam of 
atmospheric pressure is injected into the plant charge, condensation of 
steam will take place until the temperature of the still content has risen to 
that of the steam. 

Heat in conjunction with moisture soon causes the plant tissues to 
swell, the cells and pores to enlarge, and the total volume to expand. Com- 
pletely swollen seed material, for example, may have expanded by one- 
fourth of its original volume. In actual distillation, this loosening of the 
plant material may, however, be partly counteracted by the weight and 
pressure of the softened plant charge. 

An actual bursting of the plant membranes by the action of steam takes 
place probably to a limited extent only. The hot steam undoubtedly exerts 
a certain preparatory effect important for the vaporization of the enclosed 
volatile oil, but the action of steam per se is not sufficient to liberate that 
part of the oil which remains protected by resistant cell membranes. 

Influence of the Distillation Method on the Quality of the Volatile Oils. 
The quality, as well as the physicochemical properties, of a volatile oil are 
greatly influenced by the condition of the plant material (age, dried or 


fresh) and by the way distillation is carried out. Many factors enter the 
picture, viz., the method of distillation (water distillation, water and steam 
distillation, and steam distillation), the degree of comminution of the plant 
material, the quantity of the plant charge, the length of distillation, the 
pressure applied, the quality of the steam, the treatment of the distillation 
waters, whether the oil of cohobation is added to the main oil or not, etc. 

The effects of water distillation and steam distillation differ considerably, 
in that high boiling constituents of the volatile oil are recovered only in- 
completely in the case of water distillation, if the plant material is in- 
sufficiently comminuted. Even leaf material yields volatile compounds of 
high boiling point only incompletely by water distillation. Von Rechen- 
berg 28 reported that patchouli leaves yielded 3.27 per cent of volatile oil on 
steam distillation, and only 2.98 per cent on water distillation. The latter 
oil contained only a small quantity of the high boiling constituents, which 
incidentally possess also a high specific gravity and a high odor and fixation 
value. Oil constituents which are slightly soluble in water, phenols and 
certain alcohols and acids for example, are retained in the water, with the 
result that water distillation and steam distillation yield different types of 
oil, if the plant material contains only small quantities of oil. 

General Difficulties in Distillation. Essential oils consist of volatile 
compounds which are more or less sensitive to the influence of heat. It is 
doubtful, therefore, that all the volatile constituents present in the living 
plants can be isolated as such by distillation. In addition, distillation of 
certain plant materials is connected with difficulties of hydrodiffusion. The 
oil in part resinifies, and in part remains in the plant tissue. Hence every 
type of plant material requires a particular method of distillation. 

Because of these difficulties, and because of the high cost of distillation 
in certain cases (through excessive steam and fuel consumption), it has been 
suggested that such materials be extracted with volatile solvents, and the 
concentrated extracts steam distilled. The oils obtained usually contain 
small quantities of resinous and waxy matter ; such oils may be soluble in a 
certain volume of dilute alcohol, but the solutions often become turbid when 
more of the dilute alcohol is added. 

(e) Hydrodistillation of Plant Material at High and at Reduced Pressure, and 
with Superheated Steam. 

Steam Distillation of Plant Material at High Pressure. Certain plant materials 
orris root, sandalwood, cloves, caraway seed, pine needles, for example are 
occasionally distilled with steam of a pressure higher than atmospheric, in order 
to obtain a more favorable ratio of oil to water in the distillate, i.e., to shorten the 
length of distillation and to increase the total yield of oil. Purely physical con- 
siderations, a discussion of which would lead too far, show that a substantial gain 

28 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig, (1910), 441. 


can be achieved only with a pressure of several atmospheres within the retort. 
This, however, usually causes such profound decomposition of the plant material 
and of the volatile oil that the method cannot generally be applied in practice. 

The actual pressure within the retort, when using high pressure steam of 4 
atmospheres as measured in the steam boiler, is certainly less than one atmosphere 
above normal atmospheric pressure. If, notwithstanding, such modest excess 
pressure leads to favorable results primarily to a shortening of the distillation 
process the explanation must be sought in other, perhaps purely mechanical 
factors. If the steam were throttled by a valve in the gooseneck and the pres- 
sure thus increased, a manometer would indicate continuous pressure fluctuations 
within the still. These fluctuations prevent the steam from stagnating in the too 
densely packed portions of the plant charge, and seem to loosen all parts of the 
charge. This is particularly true of direct steam distillation and, to a certain 
extent, also of water and steam distillation, if the plant material has been packed 
high, and not sufficiently uniformly or tightly. Water distillation, on the other 
hand, does not seem to be affected by excess pressure. The effect of high pressure 
appears to be more pronounced when the plant material has been charged im- 
properly into the still, and when a less efficient distillation, at atmospheric pres- 
sure, has been carried out previously. 

The use of high-pressure steam for the rectification of volatile oils per se is not 
advisable, nor is it necessary, because for this purpose superheated steam gives 
better results. Xor should it be made a general practice to distill plant material 
with high-pressure steam, as this will increase the quantity of decomposition 
products in the plant material and in the oil, the degree of decomposition being 
influenced by the height of the pressure applied, the resulting rise of the tempera- 
ture, and the length of distillation. Ordinary steam distillation, even at atmos- 
pheric pressure, affects some of the constituents of the essential oil and of the 
plant material itself (the latter being even more sensitive to high pressure steam 
than the oils). The nonvolatile plant matter may thus undergo more or less pro- 
found decomposition, with accompanying formation of undesirable volatile sub- 
stances, which may considerably impair the color and odor of the oil. The dis- 
tillate may become so much contaminated with foreign matter that even rectifica- 
tion no longer yields a normal oil. (von Rechenberg). 

For all these reasons distillation with high pressure steam is not recommended, 
if the operation aims at obtaining a volatile oil containing delicate constituents. 
It may, however, be advantageous in some cases, where the distillate is to be 
further processed as with oil of camphor and steam distilled pine (stump) oil. 

Water Distillation of Plant Material at High Pressure. It is not advisable to 
employ this method, because the resulting higher temperature gives rise to decom- 
position products which impart a disagreeable "burnt" odor to the oil. Neither is 
there any appreciable gain in the ratio of oil to water in the distillate, except 
perhaps in cases where previous distillation under atmospheric pressure has been 
carried out inefficiently. 

Steam Distillation of Plant Material at Reduced Pressure. This method may be 
subdivided into two types, viz., (a) steam distillation at slightly reduced pressure, 
and (6) vacuum steam distillation at such a low pressure that the temperature 
remains just enough above that of the cooling water to permit sufficient condensa- 
tion of the steam/oil vapors. 

(a) It is a known fact that a pressure reduction within the still often shortens 
the length of distillation. Even a slight reduction may shorten the duration to 


only one-half the time required for steam distilling at atmospheric pressure. 
Von Rechenberg 24 demonstrated that this effect is caused by fluctuations in the 
steam/oil vapor pressure which, as in the case of distillation at high pressure, exert 
a continuous loosening effect upon the plant charge. 

(6) The principal advantage of steam distillation of plant material in vacuo 
consists in the pure odor of the volatile oil thereby obtained. It will be free from 
any off-odor caused by decomposition, which accompanies most oils distilled 
above 70. 

If the hydrodistillation in vacuo is not carried out with steam generated by 
boiling the water within the still (water distillation, or water and steam distilla- 
tion) but by steam generated in a separate steam boiler, a distillation with super- 
heated steam at reduced pressure will result. Even high boiling constituents of the 
volatile oil will then readily distill over; a previously air-dried plant charge, under 
these circumstances, may, however, gradually dry out until the volatile oil en- 
closed within the oil glands can no longer be vaporized, because the forces of 
hydrodiffusion no longer play their important role. It will then become necessary 
to apply saturated steam at atmospheric pressure, so that steam condensation 
within the plant charge again forms (liquid) water, which will permit the forces of 
hydrodiffusion to act anew. 

When hydrodistilling at reduced pressure it is preferable to employ spiral 
condensers rather than tubular ones, because the former can be tightened better. 
The surface of condensation should be about five times larger than when distilling 
at atmospheric pressure. This increase is necessary for several reasons: (1) The 
differential in the temperature of steam and cooling water is much smaller at 
reduced pressure. The rate of condensation, therefore, decreases. (2) The 
volume of a given quantity (weight) of steam is much larger at reduced, than at 
atmospheric, pressure. For instance the volume of 1 kg. of steam at the following 
pressures is : 

Millimeter Pressure Cubic Kfefers 

760 1.650 

380 . 3.150 

150 7.650 

76 14.530 

The velocity at which the steam enters the condenser will affect the transfer 
of heat to the cooling surface. Therefore, depending on other variables, an ap- 
propriately designed condenser (as to type, length, etc.) will have to be em- 
ployed. Too long a condenser being impractical, several spiral condensers 
connected with a T tube may be installed side by side. Since an efficient 
vacuum pump creates a higher vacuum than is actually required for the distilla- 
tion of plant material, the pressure within the still should be regulated by a valve 
permitting enough air to enter the still to sustain the desired pressure. The pres- 
sure should be measured by two manometers, one reaching into the receiver and 
one directly into the retort. 

Steam distillation of plant material in vacuo is limited in application by the fact 
that cooling and condensation of the vapors become increasingly difficult as the 
pressure and temperature of distillation are lowered. The general application of 
hydrodistillation in vacuo to plant material is restricted by another factor. With 

24 "Theorie der Gewinnung und Trennung der atherischen Ole," Leipzig (1010), 392, 


lowered pressure in the still, the partial pressure of the oil vapors decreases rela- 
tively more than that of the water vapors (steam) ; hence, the ratio of the volatile 
oil in the distillate is smaller than when distilling at atmospheric pressure. In 
other words, more steam will be consumed when hydrodistilling a certain quantity 
of oil in vacuo than at atmospheric pressure. This lower rate of vaporization of 
the volatile oil is particularly pronounced in the case of water distillation of plant 
material containing high boiling and partly water soluble constituents. (See 
below.) In this case, a multiple volume of steam (as compared with distillation 
at atmospheric pressure) is often required to attain the same yield of oil. Any 
increased steam consumption also results in higher working cost, since much more 
distillation water must be redistilled or extracted. 

When processing of plant material by water and steam distillation is practiced 
at reduced pressure, pressure variations in the still may cause loosening of the 
plant charge, so the rising steam is better saturated with oil vapors. This factor 
occasionally results in a lower consumption of steam than when working at 
atmospheric pressure. The most suitable method of distilling plant material at 
reduced pressure is u ith water and steam, provided the nature of the plant material 
permits its application. In general, it can be said that steam distillation of aro- 
matic plants, under reduced pressure, remains very limited in practice. 

Water Distillation of Plant Material at Reduced Pressure. According to es- 
tablished thermodynamic principles and to the explanation given in the preceding 
pages, hydrodistillation at reduced pressure has the effect that, with equal quanti- 
ties of conderisato, the steam volume in the distilling space, and therefore the steam 
velocity, will increase enormously as the pressure in the still is reduced. For 
example, a given quantity (weight) of totally saturated steam and benzaldehyde 
vapor fills a certain volume at atmospheric pressure (760 mm.); at 76 mm. pres- 
sure the volume \\ill be approximately ten times larger, at 31 mm. approximately 
twenty-four times larger than that occupied under atmospheric pressure. The 
velocity under which the vapor mixture rushes through the condenser increases in 
the same ratio. Hence water distillation of plants at reduced pressure is connected 
\\ith certain inconveniences with which the operator should be familiar. 

Any increase in the speed of distillation affects the purity of the distillate 
because minute plant particles are carried over mechanically. As a precaution 
against this, speed must be moderated as much as possible; flat, wide, rather than 
tall, stills should be selected for this purpose. It should also be borne in mind 
that the steam is to some extent throttled in the gooseneck (the narrowest part of 
the still). This may result in a slight back pressure within the retort, relative to 
the pressure in the receiver, which differential might easily amount to 10 mm. 

It is, therefore, advisable to adjust the speed of distillation to the tempera- 
ture prevailing within the retort. This will prevent a rise in the distillation 
temperature above a desired point. 

The great advantage of water distillation of plant material at reduced pressure 
lies in the fact that it can be carried out at relatively low temperatures e.g., 
at 50 which reduces decomposition of the essential oil. It is not advisable to 
operate at lower temperatures, because the oil vapors can then no longer be suffi- 
ciently condensed, and considerable losses of oil might occur. Furthermore, 
higher boiling, slightly water-soluble compounds are retained partially in the plant 
material and in the water, and the oil will be deficient in these constituents. 
This phenomenon, already discussed under water distillation of plants at atmos- 
pheric pressure, is even more pronounced in its effects when reduced pressure is 


employed. This very factor limits the application of water distillation in vacua 
to only a few plant materials. 

Temperatures of only 30 to 50, and the presence of water offer favorable con- 
ditions for fermentation of the plant material, for which reason distillation of this 
type should not last longer than a few hours. The oils obtained by this method 
will never possess a "still" or "burnt" odor, but rather a slight "fermented" one. 

Superheated Vapors. As was pointed out in the theoretical part of this chapter, 
a vapor is saturated so long as it remains in contact with the liquid from which it 
originates. Saturated vapors possess characteristic properties by which they 
differ sharply from vapors separated from their liquid sources. The slightest 
cooling of a saturated vapor causes partial condensation, the slightest heating 
results in increased vaporization. So long as it remains in contact with its liquid, 
a saturated vapor is seldom absolutely dry ; usually it contains admixed particles 
of the liquid in the form of spray. Moderate vaporizing, even evaporating of the 
liquid phase, carries microscopically small droplets upward into the vapor space. 
Vigorous boiling ejects larger quantities from the turbulent liquid; these are kept 
suspended by the flow of the vapors, or they drop back into the boiling liquid, 
to be replaced by new ones. Very wet vapors are more or less hazy. The trans- 
parency of a vapor, however, merely proves that it does not contain larger quan- 
tities of the liquid phase; it does not prove that the vapor is absolutely free of 
liquid, since minute droplets floating in the clear vapors are invisible to the eye. 
Their actual presence in the vapors is proved by the fact that the condensate of 
plant materials or of volatile oils is usually contaminated with dust or with non- 
volatile colored substances. 

Let us assume that we continue to heat and vaporize a liquid at constant ex- 
ternal pressure to the point where the last molecule of the liquid phase is trans- 
formed into vapor. At this very moment the vapors are still saturated, dry 
saturated. Further heating no longer induces the formation of vapors, it only 
increases the temperature of the formed vapors, with a resulting expansion of their 
volume. The vapors then become superheated. Thus, superheated vapors 
possess a higher temperature, a larger volume and a lower density than saturated 
vapors at the same pressure. Superheating of a vapor may also be interpreted as a 
heating beyond the point of saturation. Saturated vapors, as compared with 
superheated vapors at the same pressure, therefore, contain a maximum of mass, 
as well as the highest specific gravity and the lowest specific volume (the specific 
volume being the reciprocal value of the specific gravity). When comparing the 
two types of vapors at the same temperature, superheated vapors possess a lower 
pressure than saturated vapors. A saturated vapor exerts the maximum pressure 
at the given temperature. Cooling merely lowers the temperature of super- 
heated vapors, without causing condensation (as would be the case with saturated 
vapors). Only by further cooling, to and below the point of saturation, will a 
portion of the vapor be condensed. The moment a superheated vapor is brought 
into contact with the liquid phase from which it originated, vaporizing will take 
place, until the saturation point is reached once more. The superheated vapor 
thus passes into a saturated vapor, (von Rechenberg). 

Distillation of Plant Material with Superheated Steam. Relative to its weight, 
superheated steam can vaporize and entrain more volatile substances than satu- 
rated steam. In practice, steam may be superheated by passing it through fire 
tubes in a boiler in other words, through a superheater. This superheated 
steam, mixed with high-pressure and saturated steam, is then injected into the 


still beneath the grid which supports the plant material. The mixing of super- 
heated steam with saturated steam serves as a precaution against "burning" and 
decomposition of the plant material. Thus dry, slightly superheated steam is ob- 
tained. However, there remains the danger of decomposition, at least to a certain 
degree. The distillation will be shortened, but the oil yield may suffer, because 
the plant charge easily dries out as the forces of hydrodiffusion no longer play their 
important role. 

Although rectification of certain essential oils with superheated steam at 
atmospheric and especially at reduced pressure has been found valuable, its use 
in the distillation of plant material is limited, and often connected with more 
disadvantages than advantages. 

Advantages and Disadvantages of High-Pressure and Superheated Steam in 
Plant Distillation. When high-pressure or superheated steam is employed in dis- 
tillation with direct, live steam (but not in water distillation, or water and steam 
distillation), the condensation of water vapors in the plant charge may be greatly 
reduced, if not prevented altogether, except in the part of the charge along the 
walls of the retort, which usually becomes moist despite good insulation. This 
feature permits a more complete exhaustion of the plant charge. Furthermore, 
the use of high-pressure steam with its elevated temperature increases the partial 
pressure of the volatile oil, and the ratio of oil to water in the condensate becomes 
more favorable. In other words, distillation will be shortened. To exploit this 
effect of high-pressure steam, any condensed water accumulating beneath the 
steam coil in the retort must be prevented from rising above the coil, since high- 
pressure or superheated steam would then be transformed into low-pressure, 
saturated steam, of 100 direct steam distillation thus being transformed into a 
water and steam distillation. Therefore, any condensed water must be drawn off 
from time to time. Such condensed water always contains extractive matter 
dissolved and dripping down from the plant charge, and this matter has a tendency 
to undergo decomposition. Some of the resultant products are volatile and of 
disagreeable odor, and when carried over into the receiver will contaminate the 
volatile oil. As mentioned previously, not only the volatile oils themselves, but 
also the plant materials, are very sensitive to the influence of heat and easily 
decompose. This takes place even at a temperature of 100, but the effect is 
much more pronounced at a higher distillation temperature. High-pressure steam 
or superheated steam gives rise also to resinification and to the formation of in- 
soluble compounds, parts of which vaporize and distill over. Such oils are less 
soluble in dilute alcohol or, when soluble, cause turbidity on further addition of 
dilute alcohol. Hence, the use of high-temperature steam in the distillation of 
aromatic plants cannot be recommended generally. 

As was explained in our discussion of hydrodiffusion, the volatile oil enclosed 
in the cell membranes of aromatic plants must first be dissolved by hot water ; and 
then, by forces of diffusion, be brought to the surface of the plants or plant par- 
ticles, where the volatile oil may be vaporized and entrained by the passing steam. 
The exuded water must be replaced, so that the process of hydrodiffusion is not 
interrupted. The water necessary for this purpose comes partly from the mois- 
ture contained originally in the plant material itself, partly from steam condensa- 
tion (which takes place particularly at the beginning of distillation). When high- 
pressure, or dry, superheated steam is used, only that part of the volatile oil is 
vaporized which has been freed by comminution ; at the same time the moisture 
present in the plant material vaporizes, and the plant charge dries out. Then 


any oil remaining within the plant tissue can no longer reach the outside by 
hydrodiffusion, as there is no longer any water present or available ; distillation will 
therefore be incomplete, and the yield of oil subnormal, unless saturated steam of 
low pressure is injected after the application of high-pressure or superheated steam. 

There are a few cases in which distillation with superheated steam becomes 
advantageous e.g., with plants that contain much moisture (60 to 80 per cent) 
and are difficult to dry. If such material is distilled with low-pressure saturated 
steam, the high moisture content of the charge will cause much steam condensa- 
tion: the plant charge lumps and is difficult to exhaust. This can be prevented 
by applying superheated steam, a smaller or larger portion of the water within the 
plant charge then vaporizing while hydrodiffusion still functions. 

In general, it can be said that plant material containing low boiling essential 
oils is preferably distilled with low-pressure steam, whereas high-temperature 
steam recommends itself for the distillation of high boiling oils. 

(f) Field Distillation of Plant Material. In primitive countries, where 
aromatic plants grow wild, or are cultivated by natives as patch crops, essential 
oils are obtained by a form of distillation which may most appropriately be termed 
field distillation. Lack of roads prevents transport of the plant material to cen- 
trally located larger distilleries, and the distillation equipment has to follow the 
plant material into the interior of the growing region. Small portable or movable 
stills must be used ; but they serve only for a certain time of the year, and remain 
unused for the remainder of the time. They must, therefore, be low priced, sturdy, 
simple, easy to transport and to install in the fields, and simple to operate. In 
many cases this type of distillation is old; it has developed along purely empirical 
lines as an "art" inherited through generations. One should not summarily 
condemn this industry as antiquated and too primitive, however, because, in 
many instances and in view of the circumstances, a change to more modern and 
more expensive equipment is difficult, if not impossible. Indeed, such a change in 
some cases, might be for the worse, so far as prices of the oils, particularly, are 
concerned. On the other hand, this method of operation is frequently faulty, 
although it could be improved readily by only a few slight modifications. 

Distillation may be carried out either by heating the still with direct fire or 
by steam generated in a separate small steam boiler. The former is simply an 
example of water distillation, or a water and steam distillation. Direct steam 
distillation, in this case, represents a stage in the transition to larger distilleries, 
because steam distillation is economical only if the steam generator is connected 
with several stills. 

Despite the often primitive apparatus, the quality of oil resulting from water 
distillation in some instances has been good. However, the yield of oil in field 
distillation is often far below that obtained by water distillation on a large scale 
in more modern factories. The principal reason is probably that the small dis- 
tillers do not always observe the fundamental rules of efficient water distillation, 
i.e., a small plant charge and a quick distillation. Most small operators are 
inclined to charge their retorts as high as possible in order to utilize them fully; 
furthermore, the speed of distillation is usually limited by too small a condenser. 
Also, in primitive operation the plant material is seldom comminuted, although a 
thorough comminution in the case of water distillation L* often of prime importance 
for a normal yield of oil. 

The following cases of actual distillation in the field will prove to what degree 
the yield, as well as the quality, of an essential oil depends upon the method of 



distillation. They also show that in many countries production of essential oils 
remains utterly primitive, and that the introduction of better methods would 
result in a considerable improvement in the yield and quality of the oils. The 
data are cited partly from von Rechenberg's "Theorie der Gewinnung und Tren- 
nung der atherischen Ole," Leipzig, 1910, but have been confirmed by the author 
during his own investigations in the interior of China, Mexico, France, Spain and 
many other countries. 

Distillation of Lavender in France. Years ago lavender oil used to be produced 
in Southern France in numerous small distillation posts, distributed throughout 
the growing regions of the De'partements Basses- Alpes, Drome, Vaucluse, Alpes-i 
Maritimes and Var. These posts consisted of old-fashioned direct fire stills, 

Courtesy of Fritsschf Brothers, Inc., New York. 

PLATE 5. An old-fashioned direct fire still as used years ago for the distillation of lavender 

in Southern France. 

holding about 60 kg. of plants and 60 liters of water. An operation was completed 
after about 15 liters of distillation water had been collected. The action of the 
boiling water upon linalyl acetate, the main constituent of lavender oil, resulted in 
considerable hydrolysis of this ester, and the lavender oils obtained by this method 
were relatively low in esters. The introduction of water and steam distillation, 
in which the plant material is packed on a perforated grid above the boiling water, 
resulted in a marked increase of the ester content. This effect was even more 
pronounced when Schimmel & Company showed by systematic experiments in 
their modern distillery in BarrSnie (B. A.) that oils containing 50 per cent and more 
of esters could be obtained by rapid distillation with direct steam. 

Distillation of Petitgrain Oil in Paraguay. Similar conditions prevail in regard 
to the distillation of petitgrain oil in Paraguay. There, too, the leaf material 
is charged into primitive field stills and, during distillation, is partly submerged 
in boiling water. As a result, linalyl acetate, the main constituent of petitgrain 


oil, is partly hydrolyzed. For this reason, principally, the bulk of Paraguay petit- 
grain oil has an ester content averaging from 43 to 54 per cent only, whereas ex- 
periments with direct steam distillation in modern stills have proved that oils 
containing up to 80 per cent ester can be produced without too much difficulty. 

Distillation of Linaloe Wood in Mexico. The distillation of linaloe wood in 
Mexico furnishes proof that the yield and quality (physicochemical properties and 
chemical composition) of an essential oil depend a great deal upon the method of 

The trunks and branches of the felled trees are reduced to chips with axes and 
machetes. The chips are then charged into galvanized iron retorts 1.10 m. wide 
and 2 m. high. In past years water was added to the chips and distillation of each 
batch carried out for about 18 to 20 hr., the heat being supplied by an open fire 
beneath the still. Distillation of linaloe wood in past years was thus a typical 
case of water distillation. The yield of oil then varied from only 0.6 to 1.0 per 
cent, seldom exceeding 2 per cent. This low yield was undoubtedly the result 
of insufficient reduction of the wood material, and in general of water distillation 
which in this case should not be applied. 

In order to prove this contention, Schimmel & Company 25 imported Mexican 
linaloe logs to Europe and submitted the mechanically and properly comminuted 
material to direct steam distillation by modern methods. Yields ranging from 
6.0 to 11.0 per cent of oil were obtained. The resulting oils differed considerably 
from the Mexican distilled oil. The latter contained more linalool, the Schimmel 
oil more of the high boiling constituents. Evidently in Mexico the wood svas not 
sufficiently comminuted, with the result that little oil was liberated from the oil 
glands. The old Mexican method of distillation seemed to depend primarily 
upon the forces of hydrodiffusion, which means that the more water-soluble oil 
constituents such as linalool were freed from the wood, while the water-insolu- 
ble compounds remained, and partly resinified during the long hours of distillation. 

During the years of World War II, the author visited the linaioe oil producing 
regions in Mexico and observed that the method of distillation has been improved 
considerably. Today the stills are equipped with a perforated tin plate, 60 cm. 
from the bottom of the still, the perforated plate supporting the chipped wood 
material. The section below the plate contains water which does not come in 
contact with the charge. Thus we have here a typical case of water and steam 
distillation, the water being heated with an open fire beneath the still. As a re- 
sult of this method of distillation, the yield of oil today ranges from about 2.2 to 
2.6 per cent for chips, and from about 3.5 to 4.4 per cent of oil from sawdust. 
Each operation now requires 8 to 9 hr. of distillation. Each charge consists of 
230 kg. of wood material. In the states of Puebla and Guerrero, it is customary 
to reduce the linaloe wood into chips, while the producers in the state of Colima 
reduce the wood into coarse saw dust and thereby obtain a considerably higher 

Distillation of Cassia Leaves and Twigs in China. Large quantities of cassia 
oil are produced yearly in the south Chinese provinces of Kwangsi and Kwangtung. 
The stills used by the natives are of antiquated Chinese design. Their principal 
fault lies in the loose connection of the joining parts and in the insufficient con- 
densers. A charge consists of about 60 kg. of cassia leaves and twigs, and ap- 
proximately 180 liters of water, which is brought to a boil by an open fire beneath 

* Ber. Schimmel & Co., October (1907), 55. 


the retort. Distillation of one batch lasts about 2 2 hr. The conclensate is 
collected in a series of pots, arranged in the form of cascades. Cassia oil is heavier 
than water. 

The yield of oil from leaves alone averages 0.10 to 0.13 per cent, and that from 
a mixture of 70 per cent leaves and 30 per cent twigs 0.15 to 0.17 per cent. 

Because of insufficient cooling in the condenser, the distillate usually runs quite 
warm, if not hot, and therefore a part of the oil remains emulsified or suspended 
in the water. The milky distillation water is added to the next batch of plant 
material, a procedure which entails a certain loss of oil by evaporation and par- 
ticularly by resinifi cation. The principal cause of the subnormal yield of oil lies 
in the use of water distillation in the case of cassia leaves or, more exactly, in the 
faulty method of carrying it out. Cassia leaves possess a leathery consistency, 
remaining tough even in boiling water, and, therefore, if not sufficiently com- 
minuted, cannot be completely exhausted by mere water distillation. 

In order to study the problem by practical experiments, Schimmel & Com- 
pany 26 imported dried cassia leaves and twigs from China, and submitted them to 
distillation tests in modern direct steam stills. The leaves yielded 0.7 to 0.8 per 
cent of oil, the twigs 0.2 per cent. These percentages are much higher than those 
obtained by the native Chinese distillers. True, the plant material arriving in 
Europe had lost considerable weight from drying; the Chinese producers use fresher 
leaves and twigs. Assuming the loss of moisture through drying to be about 50 
per cent of the original plant weight, the yields of oil, as calculated upon the fresh 
plant material would, therefore, be as follows: 

Fresh leaves, distilled in Europe 0.35 to 0.40% 

70% fresh leaves plus 30%, fresh twigs, distilled in Europe 0.31 to 0.34% 

Fresh leaves, distilled in China 0.10 to 0.13% 

70% fresh leaves plus 30% fresh twigs, distilled in China 0.15 to 0.17% 

This differential in yield is actually even greater, because as a result of the long 
transport and desiccation, a part of the cinnamic aldehyde, the main constituent 
of cassia oil, had been oxidized. 

These experiments prove that the native distillation of cassia oil is carried 
out in such a primitive and faulty way that quantities of oil amounting to about 
twice the actual production per year are lost in the residual plant material. The 
use of water distillation is not the only cause of this waste. Another reason for 
the subnormal oil yield obtained by the Chinese distillers, appears to be this: 

Because of insufficient condensation of the steam/oil vapors, distillation must 
be carried out very slowly. The motion of the plant charge in the boiling water is, 
therefore, correspondingly slow, and the water between the agglutinating leaves 
cannot circulate sufficiently. The volatile oil, which diffuses from the leaves into 
the boiling water partly dissolves therein, and remains, in part, suspended between 
the agglutinated leaves, without being vaporized by contacting steam bubbles. 
In other words, presence of the liberated, but not vaporized, oil inhibits further 
diffusion of oil from the leaves. Evidently, the forces of diffusion can come into 
play only where there exists a differential in concentration. In other words, the 
quicker the oil solution is removed from the surface of the leaves, and the quicker 
the oil is vaporized, the more forcibly diffusion acts. Otherwise an equilibrium in 
the charge will result, and the distillate will contain very little oil, in spite of the 

M tier. Schimmel & Co., October (1896), 11. 


fact that considerable quantities of oil are still retained in the leaves. This also 
explains the relatively short length of distillation in the native cassia stills; the 
distillers simply stop the operation when they no longer see oil distilling over. 
It should not be surprising at all that the admixture of twigs to the leaves increases 
the oil yield, although the actual oil content of twigs amounts to only one-quarter 
that of the leaves. By the addition of twigs the charge simply becomes looser 
and the interspaces between the leaves larger. The boiling water, even though 
moving slowly, can then penetrate the interspaces much better and carry away 
the oil as it diffuses from the leaves; the oil is thus conducted toward the surface 
and vaporized. 

(g) Rectification and Fractionation of Essential Oils. Many essential 
oils, when distilled from the plant material, are contaminated with volatile 
products arising from the decomposition of complex plant substances, under 
the influence of hot water or steam. This takes place especially in the case 
of water distillation in directly fired stills if, through carelessness, the plant 
charge "burns" on contact with the retort walls touched by the fire. Some 
of these decomposition products are gaseous e.g., hydrogen sulfide and 
ammonia ; others such as methylalcohol, acetaldehyde, acetone, and acetic 
acid are very soluble in water. Therefore, they occur mainly in the distil- 
lation water, and accumulate in the water oil when cohobating the distilla- 
tion waters. For this reason the water oil usually possesses a rather dis- 
agreeable odor and should not be mixed with the main oil without previous 
careful purification. 

Occasionally the main oil, too, contains as normal constituents substances 
of somewhat objectionable odor e.g., certain aldehydes or sulfur com- 
pounds. In order to improve the odor of such oils, they must be freed from 
these undesirable compounds by redistillation. This applies also to crude 
oils possessing too dark a color, which is often due to the presence of metals, 
or to fine plant dust carried over by the steam, especially when the live steam 
enters the still too forcefully or too rapidly. When the steam is injected 
more slowly, the plant charge becomes somewhat wet by steam condensation, 
and the dust particles are retained by the plant material. 

Redistillation of a volatile oil does not necessarily bring about an im- 
provement in its quality ; in fact, in some cases the contrary may be true. 
This is particularly so with oils possessing easily saponifiable esters, such as 
bergamot or lavender oil. Linalyl acetate, the main constituent of these 
oils, is hydrolized by boiling with water, or by rectification with live steam, 
the freed acetic acid causing further hydrolysis. 

For the redistillation of a volatile oil two general methods are employed, 
viz., rectification and fractionation, both of which will be described in more 

Rectification aims at the separation of volatile and nonvolatile compounds 
if a lighter colored oil is desired ; the coloring matter remains as residue in 


the still. This may be achieved by dry distillation in vacuo or by hydro- 
distillation (with live steam or by boiling with water). Hydrodistillation 
can also be carried out at reduced pressure. 

Fractionation or fractional distillation aims at separating the volatile oil 
into various fractions, according to their boiling points and odor. In most 
cases this is achieved by dry distillation in vacuo. A volatile oil should 
never be fractionated at atmospheric pressure, because the high tempera- 
tures involved cause decomposition and resinification, the distillate then 
possessing an odor and physicochemical properties quite different from those 
of the original oil. The boiling temperature can be considerably lowered by 
distilling the volatile oil at greatly reduced pressure, a process also referred 
to as dry distillation in vacuo. Decomposition of the oil is thus reduced to a 

Rectification of Essential Oils. Rectification with water vapors (steam) 
is the older of the two methods. Retorts employed for this purpose are 
usually spherical, made of copper, heavily lined with tin, and heated with a 
steam jacket. To prevent coloring of the oil by contact with metal, the 
gooseneck and condenser should be made of pure tin or of heavily tinned 
copper. Condenser and oil separator should be installed at such a height 
that, if it seems desirable, the distillation water can return automatically 
into the retort during distillation. Water is poured into the retort to a 
level of about 4 or 5 in. above the steam jacket and the oil added. Some 
oils peppermint and caraway seed oil, etc. easily assume a disagreeable 
by-odor when coining in contact with the hot still walls. This by-odor, 
known as "still odor," may be partly avoided by covering the steam jacket 
or the steam coils with sufficient water before starting the operation. The 
water level must be retained throughout the distillation. Flat-bottomed 
steam jackets are, therefore, preferable for the rectification of volatile oils. 
A steam coil, provided with many small holes and inserted close to the bot- 
tom of the retort, serves for direct heating with live steam (if this modifica- 
tion is preferred) and also for steaming out (cleaning) the still after comple- 
tion of the operation. Steaming out is usually preceded by a washing with 
hot water, soap or alkali solution or with volatile solvents. 

The speed of rectification is influenced by several factors. If the dis- 
tillation waters should return automatically into the retort, the speed might 
be limited by excess pressure developing within the retort ; in fact, this might 
altogether prevent the distillation water from returning automatically into 
the retort. If the distillate should be absolutely colorless, rectification must 
be carried out very slowly; otherwise very fine droplets, often invisible in 
the vapors, are carried into the condenser and oil separator, and color the 


As has been said, some crude volatile oils contain compounds of objec- 
tionable odor, which are often more soluble in water than the main consti- 
tuents. This fact can be taken advantage of by rectifying the volatile oils 
through hydrodistillation : the distillation water containing most of these 
objectionable compounds is not returned to the retort, but the water dis- 
tilling off must be replaced by fresh water ; or, instead of heating indirectly, 
direct live steam may be injected into the oil charge. In the latter case 
only sufficient water to cover the steam coil need be charged into the retort. 
However, the danger of oil droplets being carried over mechanically be- 
comes somewhat greater as the live steam entering the retort has a tendency 
to whirl the oil upward. A short rectification column may be of service in 
this respect. When rectifying a volatile oil with direct live steam at 
atmospheric pressure (in other words, with low-pressure steam), some steam 
will be condensed to water continuously within the retort. The distillation 
water, in this case, cannot be returned into the retort, but must be coho- 
bated in another apparatus or extracted with volatile solvents. Actually, 
rectification of a volatile oil with direct steam of low pressure has all the 
characteristics of a water distillation, because steam continuously separates 
water as condensate within the retort. If, however, high-pressure live 
steam (10 atmospheres for instance) is injected into a well-insulated still, 
condensation of water may be prevented, provided the steam has been 
carefully dried prior to its entering the still. The distillation then becomes 
a superheated steam process, because saturated, high-pressure steam, on 
expansion, changes into superheated steam. In other words, distillation 
of a volatile oil purely by live steam is not practicable. It turns either into 
a distillation with superheated steam or into a water distillation, the latter 
with the modification that there will be only a little water within tho rotort. 

The quantity of oil to be charged into a rectifying still depends upon the 
final purpose of the rectification. If the oil is only to be decolorized, very 
little oil need be let into the retort, the vaporizing oil being replaced con- 
tinuously as new oil is pumped in. This method offers the advantage that 
the contact of oil and steam is shortened to a minimum, only a small quan- 
tity of oil being in the retort at one time. A prolonged contact of volatile 
oil with boiling water or steam at atmospheric pressure is likely to cause 
considerable decomposition, resinification, and chemical action, such as 
hydrolysis of esters, etc. 

As has been explained, rectification aims also at freeing the oil from dis- 
agreeable by-odors. If these impurities possess a low boiling point in 
other words, if they boil below the main portion of the oil they can be 
removed in the foreruns of the distillate. Foreruns are then separated so 
long as they exhibit the objectionable odor. Since a forerun usually amounts 
to only a small percentage of the total oil, it should be distilled off very 


slowly. The total amount of oil charged in the still, however, must always 
be so measured that it can be processed within one day. In order to utilize 
the capacity of a small still to the fullest, rectification is best carried out 
with direct live steam ; otherwise a part of the retort must be occupied by the 
water necessary for distillation. After the forerun has distilled over, the 
speed or rate of distillation may be increased to whatever degree condenser 
capacity and purity of the distillate will permit. 

If the volatile oil to be rectified contains impurities boiling higher than 
the main part of the oil, the main run should be distilled off slowly, as this 
will permit better separation and a diminution of the last runs. The speed 
of distillation may be increased when the last runs containing the impurities 
start to distill over. To achieve a more complete separation of the foreruns 
and last runs, a fractionation column may be used and, if necessary, a 
dephlegmator above the column. Such a dephlegmator causes partial 
condensation, which affects the higher boiling constituents more than the 
lower. It thus becomes possible to reduce the quantity of the forerun and 
to increase the quantity of the main run. As was explained under "Theories 
of Distillation/' rectification columns are equipped with perforated trays, 
often with Raschig rings or porcelain balls. Columns filled with rings or 
balls have a practical advantage over columns equipped with bell or sieve 
plates, in that the former retain less condensed liquid and, therefore, exert 
less pressure upon the vapors in the still. 

The composition of the condensate, i.e., the average oil content of the 
steam and vapor mixture, depends primarily upon the boiling point or the 
vapor pressure of the oil constituents. The lower the normal boiling point 
in other words, the higher the vapor pressure of the oil constituents at the 
prevailing temperature of distillation the greater will be the ratio of oil 
in the condensate. The average oil content of the steam and vapor mixture 
in the distillation of oil is much larger than it is in the distillation of plant 
material. (See section on "Steam Consumption in Plant Distillation/') 

Fractionation of Essential Oils. We shall now proceed to a description 
of the fractionation, which is carried out at reduced pressure (partial vacu- 
um) and usually by distilling the oil alone, without leading water into the 
retort or injecting live steam into the oil. This process of dry distillation 
in vacuo is widely applied in the essential oil industry today. By its means 
pressure can be so far lowered that temperature has no longer any marked 
influence upon quality. The pressure should not be higher than 5 to 10 
mm. Hg as measured in the still above the boiling liquid. How far the tem- 
perature of some oil constituents can be reduced is shown by this example: 
linalool, the main constituent of linaloe oil, boils at a temperature of 198 


at atmospheric pressure (760 mm.), and at: 

105.4 at 30 mm. pressure 
97.2 at 20 mm. pressure 
84.4 at 10 mm. pressure 
72.8 at 5 mm. pressure. 

In practice, any further lowering of the pressure requires that distillation 
be carried out very slowly; it also necessitates an efficient vacuum still, 
absolutely airtight joints, and an effective condenser, so that the low boiling 
constituents of the volatile oil may be recovered, and not lost in the vacuum 
pump. In the case of almost every vacuum distillation, small quantities 
of vapors escape into the pumps, especially if the vacuum still is not abso- 
lutely tight. The air leaking into the still has a tendency to carry along 
some volatile oil vapors that may not always be condensed in the condensers. 
It is advisable, therefore, to insert an absorption vessel, filled with neutral 
substance which absorbs the vapors, between the oil receiver and the 
vacuum pump. 

In order to distill over the highest boiling oil constituents in vacuo, 
temperatures of 150 to 200 are often necessary. Such temperatures can 
be obtained by the use of an oil bath which surrounds the lower part of the 
retort; in a corresponding steam jacket very high pressure or superheated 
steam would be required. The oil bath offers the advantage that the heat 
transmission between the two liquids is more gradual than that between 
superheated steam and volatile oil. Under these circumstances hydrocar- 
bons possessing boiling points up to 300 (at atmospheric pressure) can be 
distilled off, provided any condensation of oil vapors along the upper walls 
of the retort is prevented by good insulation. 

Between the pressure in the receiver and that within the retort there 
exists always a differential of a few millimeters. If the pressure in the closed 
receiver is 1 to 2 mm., the pressure in the vacuum still itself (retort) will be 
about 5 mm., provided the vapor development remains moderate. The 
faster the distillation, the lower will be the performance of the vacuum 
pump; the narrower the condenser tubes, the greater will be this pressure 

The stills serving for vacuum distillation of volatile oils are spherical, 
sufficiently strong to withstand at least atmospheric pressure, made of 
copper and heavily tinned on the inside, with gooseneck, condenser tubes 
and oil receivers also tinned. A small and strong glass window permits 
watching of the boiling liquid within the retort. All joints must be abso- 
lutely airtight. A jacket around the lower half of the retort forms an oil 
bath or a steam bath for heating with high-pressure steam (for at least 75 Ib. 
jacket working pressure). A column directly above the still, equipped with 


plates, or filled with Raschig rings, or with other packing materials, provides 
for better fractionation of the boiling liquid (see "Theories of Distillation"). 
The oil receiver consists of two closed, strong vessels with vertical glass tubes, 
through which the level of the liquid within each receiver can be gaged. 

PLATE C. Vacuum stills at Fritzschc Brothers, Inc., Clifton Factory, Clifton, N. J. 

These receivers arc tightly connected with the condenser outlet through a 
three-way stopcock, which permits one receiver to remain under vacua and 
to collect the fraction distilling over at a given temperature, while the other 
receiver may be opened to draw off the previous fraction. Pressure manom- 
eters on the retort and on the oil receivers indicate the pressure within the 
retort and within the oil receivers. One thermometer held by a nipple 



reaches within the retort and ends above the boiling liquid, whereas another 
thermometer registers the temperature on top of and inside of the fractiona- 
tion column. An airtight suction line connects the receivers with the vacu- 
um pump which should be of high efficiency. 

The still shown in Fig. 3.22 serves for the dry (without direct steam) 
vacuum distillation (fractionation or rectification) of essential oils. Heat- 


I I 


FIG. 3.22. Dual-purpose essential oil still. 

ing is achieved by a steam jacket (or oil bath if so desired). The rectifica- 
tion column can be by-passed. Provision is also made for the rectification 
or fractionation of essential oils by the use of direct steam at atmospheric 
pressure. In this case, the distillation waters may be automatically re- 
turned to the still (cohobated). The same still may be used for the prepara- 
tion of terpeneless oils. 


Inadequacies of Hydrodistillation. A comparative summary of the advantages 
ind disadvantages associated with hydrodistillation of volatile oils and with dry 
listillation in vacuo would reveal, according to von Rechenberg, an almost general 
superiority of hydrodistillation over the latter method. Depending upon the 
nature of the compound to be vaporized, it is possible to adjust the temperature of 
hydrodistillation to any desired level. The use of dry vacuum distillation remains 
limited, because high boiling compounds decompose below their boiling points, 
even in vacuo. Vacuum distillation with superheated steam is more advantageous 
in this respect. On the other hand, the use of hydrodistillation is restricted for 
several reasons: 

1. As in the case of dry vacuum distillation, the compound to be vaporized 
should be distilled in liquid form, or should at least melt below the temperature 
of distillation. However, solid compounds, and even those with very high boiling 
points, can be vaporized by steam, provided they are reduced to a moderately 
small size. Comminuted particles should be properly packed on perforated grids 
within the retort, so that the rising steam penetrates the mass uniformly, just as 
with plant material. 

2. Hydrodistillation cannot be applied to substances which, even at low tem- 
peratures, react with water, or are hydrolyzed by water (esters, etc.). 

3. Solubility in water, as well as decomposition by water, may, under certain 
circumstances, present an insurmountable obstacle to the use of hydrodistillation. 
This is particularly so if the compound to be distilled is high boiling (aside from 
being water soluble) or, in the case of plant distillation, if the plant material con- 
tains only very small quantities of the water-soluble constituent. Solubility in 
water lowers the vapor pressure of the compound and reduces its capability for 
vaporization; in other words, relatively much more steam will be required to 
vaporize the same quantity of oil. Since this lowering of the vapor pressure 
depends upon the quantity of \\atcr present, water soluble and high boiling com- 
pounds or corresponding plant matter should be distilled with steam, and not 
with boiling water. For instance, if it were practically possible to distill rose 
floweis \\ith steam, the phenyl ethyl alcohol would probably not be retained by 
the flowers or by the residual still waters. 

Solubility in water not only reduces the rate of evaporation, it also impedes 
the separation of the oil from the distillate. For this very reason the aroma of 
many flowers cannot be isolated by distillation. Any odoriferous compound is 
also volatile ; any compound which, of itself, dissipates vapors into the air should 
yield the same, if not a larger quantity to steam, and particularly at a temperature 
of distillation higher than that of the air. The difficulty is only that the small 
quantity of volatile substances cannot be isolated from the large volume of dis- 
tillation waters. 

(h) Hydrodistillation of Essential Oils at High and at Reduced Pressure, and 
With Superheated Steam. 

Water Distillation of Essential Oils at Reduced Pressure. This type of distilla- 
tion is used to prevent decomposition of the volatile oil, because by its use even 
easily hydrolyzed esters are retained intact. With certain oils the method gives 
most favorable results. 

On the other hand, it should be kept in mind that the rate of vaporization of 
water-soluble and high boiling constituents decreases as their boiling point and 
degree of water solubility increase. Stated differently, in the water distillation of 


essential oils at reduced pressure, the ratio of oil to water in the distillate is even 
more unfavorable than when water distillation of the same products at atmospheric 
pressure is practiced, because any lowering in the external pressure reduces the 
vapor pressure of all high boiling compounds relatively much more than that of 
water (steam). Also, the differential between the temperature of distillation and 
that of the cooling water in this case is slight; therefore, considerable oil losses 
may be caused by evaporation, particularly when the temperature differential is 
still further reduced by any excessive and unnecessary lowering of the distillation 
pressure. The same conditions prevail here as with hydrodistillation of plant 
materials at reduced pressure. 

To achieve a high rate of distillation when hydrodistilling volatile oils at re- 
duced pressure, the empty space above the liquid in the vacuum still should be 
kept sufficiently large to permit the still content to boil without foaming into the 
condenser. In addition, the condenser surface must be larger (about five times 
larger than that required for distillation at atmospheric pressure). In the case 
of vacuum distillation, the efficiency of the condenser is considerably reduced by 
the high speed at which the steam and oil vapors rush through the tubes, and also 
by the fact that with lower temperatures of distillation the capacity of heat ab- 
sorption by the cooling water diminishes. 

In general, it can be stated that hydrodistillation at reduced pressure is es- 
pecially suitable for the rectification of liquids that possess medium volatility and 
do not withstand heating, as well as for the purification of high boiling mixtures 
which are to be freed from lower boiling impurities. The method can also be 
used for removing traces of a solvent from an extract. Hydrodistillation can be 
conducted at as low a temperature and pressure as the temperature and the 
efficiency of the condenser permit. 

Water Distillation of Essential Oils at High Pressure. Pressure within the 
retort can be increased by inserting a throttling valve into the tube (gooseneck) 
connecting the retort with the condenser. When operating at a pressure above 
atmospheric, the unfilled space in the retort above the charge should be sufficient 
to prevent foaming over of the still content. The use of live steam is preferable, 
because refilling the still with water during the operation offers some difficulties. 
When heat is first applied to the retort, no excess pressure must be applied until 
all air has escaped from the still. 

Water distillation of volatile oils at high pressure is useful for certain purposes 
for instance, for the hydrolysis of esters, if so desired. This modification, 
however, by no means represents a general method of rectification. Relative to 
the steam pressure, the vapor pressure of higher boiling oil constituents increases 
more as the temperature rises; thus the ratio of oil in the distillate will be more 
favorable. However, from this angle, and from the practical point of view, water 
distillation at high pressure is not as effective as distillation with superheated 
steam, because the latter method vaporizes more oil without necessitating the 
high pressure of the former method. 

Distillation of Essential Oils with Superheated Steam. This occurs when the 
steam in the steam/vapor mixture rising from the oil is superheated. As was 
stated previously, this condition of the water component in the steam/vapor 
mixture is of great importance for the vaporization of oil. The same unit space 
occupied by a mixture of oil vapors and steam will contain relatively a much 
smaller quantity of steam, in a superheated state, than it would contain of 
saturated steam. 


In actual practice, steam can be superheated by two methods: 
1. By superheating within the retort. 

The volatile oil is poured into the retort (without addition of water) and 
through a steam jacket or closed steam coil or oil bath, heated above the boiling 
point of water at the corresponding pressure. If saturated but dry steam is 
injected into the oil and thoroughly distributed, the steam will be superheated in 
the hot oil layer. 

2. By superheating outside of the retort. 

The steam is superheated in a special oven before it enters the retort and, as 
such, is injected into the oil, which does not have to be specially heated. 

A combination of the two methods increases effectiveness of each. The stills 
serving for distillation of volatile oils with superheated steam should be con- 
structed high with a small diameter; they should be well insulated, and provided 
with a steam jacket and a many-coiled perforated steam pipe. These precautions 
permit the injected steam to assume the temperature of the heated oil and to 
become thoroughly saturated with its vapors. When a distillate of high purity 
is desired, the force of distillation should be moderate in other words, the quan- 
tity of the injected steam should be reduced. This is especially important in the 
case of vacuum distillation with superheated steam. A reduction in the rate of 
the injected steam also permits a more thorough saturation of the steam with oil 

In general, it can be stated that distillation with superheated steam is par- 
ticularly valuable in the case of those volatile oils or oil constituents which are 
partly soluble in water, because only a small quantity of water (steam) is required, 
and this stays in contact with the oil to be vaporized. The vaporizing liquid, 
therefore, act* like a water-insoluble compound. The method is well adapted to 
the distillation and purification of benzyl alcohol, cinnamic alcohol, phenyl ethyl 
alcohol, etc. in other words, to all high boiling and chemically stable compounds 
which contain higher boiling impurities. 

Distillation of Essential Oils with Superheated Steam at Reduced Pressure. In 
the above described process, the steam can be superheated inside or outside of the 
still. An important modification, however, consists in connecting the retort and 
the closed oil/ water separator (receiver) with a vacuum pump so that the oil 
vaporizes in the retort at reduced pressure. By this means it is possible to regu- 
late the temperature of the oil vapors at will. According to the chosen tempera- 
ture, the vapors will be more or less superheated which means a more favorable 
ratio of oil in the distillate than is the case when the oil is merely steam distilled 
without superheating. For example, by heating the oil charge in the retort 
indirectly with steam of 10 atmospheres pressure, by injecting dry live steam 
of high pressure very slowly into the oil at the same time, and by carefully adjust- 
ing the vacuum pump and the direct steam inlet to a distillation pressure of 30 to 
40 mm. at a temperature of about 160 within the retort, even high boiling com- 
pounds such as glycerin, palmitic and oleic acid will distill over in ample quantities. 
For the vaporization of high boiling substances, this method therefore exceeds 
even dry vacuum distillation in efficiency. As for every type of hydrodistillation 
in vacuo, it is necessary to provide for sufficiently large condensers, and to inject 
the direct steam very slowly into the oil charge, so that no foaming takes place, 
and the distillate will not be contaminated with impurities mechanically carried 
over, (von Rechenberg). 



As was stated in the section on "Distillation," most essential oils are to- 
day isolated from the respective plants, or parts of plants in which they 
occur, by the process of distillation. A few essential oils i.e., those present 
in the peels of citrus fruit can be, and in large part are, obtained by cold 
pressing, which yields products of superior quality. 

In our discussion of distillation it was emphasized that the process of 
distillation suffers from several inadequacies: the relatively long action of 
steam or boiling water on the plant material affects some of the more delicate 
constituents of the oil deleteriously ; hydrolysis, polymerization and resinifi- 
cation may and do take place; high boiling constituents, especially if some- 
what soluble in water, are not carried over by steam, and are therefore lack- 
ing in the distilled oil. Other constituents dissolve partly in the distillation 
water, and cannot readily be recovered. As a result of all these factors, a 
distilled oil does not always represent the natural oil as it originally occurred 
in the plant. 

A few types of flowers and this is the case with some very delicate 
ones yield no direct oil at all on distillation. The oil is either destroyed 
by the action of steam, or the minute quantities of oil actually distilling 
over are "lost" in the large volume of distillation water from which the oil 
cannot be recovered. This applies to jasmine, tuberose, violet, jonquil, 
narcissus, mimosa, acacia, gardenia, hyacinth and a few others. When 
hydrodistilled, these flowers yield either practically no oil, or in such low 
yield, or of such inferior quality, that for all purposes it is useless. There- 
fore, flowers of this type must be processed by methods other than distilla- 
tion. This fact was recognized empirically hundreds of years ago when 
such flowers were treated by maceration in cold or hot fat, which process 
yielded fragrant pomades. From this primitive beginning there developed 
in the Grasse region of Southern France, in the course of many years, a 
highly specialized industry, employing the processes of maceration and of 
enfleurage and, for the last forty years, the modern process of cold extraction 
with volatile solvents. Despite similar, but much less important develop- 
ments in other parts of the world (Bulgaria, Egypt, Algeria, Sicily, Calabria, 
Madagascar, etc.), Grasse has remained the center of this picturesque and 
charming industry, which today supplies the perfume manufacturers with a 
great variety of highly prized so-called "natural flower oils." Representing 
the authentic scents as exhaled by the flowers, these flower oils are the finest 
and most delicate ingredients at the disposal of the modern perfumer, en- 
abling him to create masterpieces of his art by skillful application and 

The term "natural flower oil," as used today commercially, does not 


include the distilled essential oils; it applies only to flower oils obtained by 
the methods of enfleurage, maceration and extraction with volatile solvents, 
which will be described later in detail. A few oils--e.g., those derived from 
rose petals and from the blossoms of the sour (bitter) orange tree can be 
isolated either by distillation or by extraction. The oils are then called 
essential oils and natural flower oils, respectively, the latter reproducing and 
representing the original scent of the flowers in a more complete way. It is 
principally the elaborate apparatus required and the higher cost of manu- 
facturing which prevent a more general adaptation of the process of ex- 


In the Grasse region of Southern France, flowers were processed by this 
method long before the modern method of extraction with volatile solvents 
was introduced. Generations ago Grasse, an ancient hill town located on 
the southern slopes of the Alpes-Maritimes and facing the Mediterranean, 
became the center of extensive flower plantations and, subsequently, of the 
French perfume industry. Grasse, like few places in the world, is favored 
by a mild climate, southern exposure and protection against north winds. 
There the cultivation of flowers for the extraction of their scent became a 
highly specialized agricultural occupation, passed down from generation to 

/ In the early days of perfumery, flower scents were extracted with fats, 
and the alcoholic washings of the perfumed fats represented the so-called 
floral extraits. These, blended with certain distilled essential oils, and tinc- 
tures, constituted the old-style perfumes. In the course of years this 
simple beginning led to our modern perfume industry with its wealth and 
variety of raw materials. 

Despite the introduction of the modern process of extraction with vola- 
tile solvents, the old-fashioned method of enfleurage as passed on from father 
to son, and perfected in the course of generations, still plays an important 
role. Enfleurage on a large scale is today carried out only in the Grasse 
region, with the possible exception of isolated instances in India where the 
process has remained primitive. 

The principles of enfleurage are simple. Certain flowers (e.g., tuberose 
and jasmine) continue the physiological activities of developing and giving 
off perfume even after picking. Every jasmine and tuberose flower re- 
sembles, so to speak, a tiny factory continually emitting minute quantities 
of perfume. This phenomenon was first studied by Passy 27 and later by 
Hesse. 28 Fat possesses a high power of absorption and if brought in contact 

27 Compt. rend. 124 (1897), 783. Bull. soc. chim. [3], 17 (1897), 519. 
"Ber. 34 (1901), 293, 2928; 36 (1903), 1465; 37 (1904), 1462. 


with fragrant flowers readily absorbs the perfume emitted. This principle, 
methodically applied on a large scale, constitutes enfleurage. During the 
entire period of harvest, which lasts from eight to ten weeks, batches of 
freshly picked flowers are strewn over the surface of a specially prepared 
fat base (corps), left there (for 24 hr. in the case of jasmine and longer in the 
case of tuberose), and then replaced by fresh flowers. At the end of the 
harvest the fat, which is not renewed during the process, has become quite 
saturated with flower oil. The latter is finally extracted from the fat with 
alcohol and then isolated. 

(a) Preparation of the Fat Corps. The success of enfleurage depends to 
a great extent upon the quality of the fat base employed. Utmost care 
must be exercised when preparing the corps. It must be practically odorless 
and of proper consistency. If the corps is too hard, the blossoms will not 
have sufficient contact with the fat, curtailing its power of absorption and 
resulting in a subnormal yield of flower oil. On the other hand, if too soft, 
the corps has a tendency to engulf the flowers so that the exhausted ones are 
difficult to remove and retain adhering fat, which entails considerable 
shrinkage and loss of corps. The consistency of the corps must, therefore, 
be such that it offers a semihard surface from which the exhausted flowers 
can easily be removed. Since the whole process qf enfleurage is carried out 
in cool cellars, every manufacturer must prepare his corps according to the 
temperature prevailing in his cellars during the months of the flower harvest. 

Many years of experience have proved that a mixture of one part of 
highly purified tallow and two parts of lard are eminently suitable for 
enfleurage. This mixture assures a suitable consistency of the corps in 
conjunction with high power of absorption. The author carried out a series 
of experiments with various mixtures of vegetable fats, especially hardened 
vegetable fats which do not easily turn rancid. He also experimented with 
all kinds of antioxidants and glycoside splitting compounds, incorporating 
them into the corps before enfleurage. The result was a variety of interest- 
ing qualities and widely different yields of flower oils, but the highest quality 
of floral oils most true to nature resulted from the old-fashioned mixture of 
lard and tallow. 

Mineral oils, too, have been suggested as bases for enfleurage work, and 
on a limited scale have been practically employed; but they offer no real 
advantage because their power of absorption is very small as compared with 
that of animal fats. Furthermore, it is exceedingly difficult to extract and 
isolate small quantities of absorbed flower oils from the mineral oils with 
alcohol or by other means. 

Many other substances have been suggested as bases for enfleurage, 
and have been patented for this purpose, but none so far has attained any 
wide commercial application. For instance, according to French Patent 


836,172, January 12, 1939 (I. G. Farbenindustrie A.-G.), 29 essential oils 
and natural flower oils are extracted by treatment of the plant material 
with esters of polyhydric aliphatic alcohols, containing at the most 6 carbon 
atoms, with fatty acids of high molecular weight, as obtained by oxidation of 
paraffin hydrocarbons of high molecular weight. Thus esters of glycol, 
glycerol, erythritol, mannitol, hexitol or trimethylolpropane may be used. 

The fat corps is prepared in the Grasse factories during the winter months 
when they are not busy with the processing of flower crops. The crude 
pieces of tallow and lard, mostly of French and Italian origin, are purified 
according to a tedious old-fashioned method. The crude fats are carefully 
cleaned by hand, all adhering particles of skin and blood vessels removed, 
then crushed mechanically and finally beaten in a current of cold water. 
After all impurities have been removed, the fat is melted gently on a steam 
bath. Small quantities of benzoin (0.6 per cent) and alum (0.15 to 0.30 
per cent) are then added. This preservation is very important, as otherwise 
the corps will turn rancid during the hot summer months. While benzoin 
acts as a preservative, the adding of alum causes impurities to coagulate 
during the heating ; when rising to the surface they can be skimmed off with 
a spoon. The warm fat is filtered through cloth, then left to cool and stand, 
so that any water may separate. 

(During the past years chemistry has made great progress in regard to 
antioxidants for fats and oil, several of which could undoubtedly be used for 
preservation of the enfleurage corps employed in the Grasse region.) 

The fat corps thus prepared is white, of smooth, absolutely uniform 
consistency, free of water and practically odorless. If well prepared and 
properly stored, it will resist rancidity for several years. 

Some manufacturers also add small quantities of orange flower or rose 
water when preparing the corps. This seems to be done for the sake of 
convention. Such additions somewhat shade the odor of the finished prod- 
uct by imparting a slight orange blossom or rose note. 

(b) Enfleurage and Defleurage. Every cnfleurage building is equipped 
with thousands of so-called chassis, which serve as vehicles for holding the fat 
corps during the process. A chassis consists of a rectangular wooden frame 
2 in. high, about 20 in. long and about 16 in. wide. The frame holds a glass 
plate upon both sides of which the fat corps is applied with a spatula at the 
beginning of the enfleurage process. When piled one above the other the 
chassis form airtight compartments with a layer of fat on the upper and 
lower side of each glass plate. 

Every morning during the harvest the freshly picked flowers arrive, and 
having first been cleaned of impurities, such as leaves and stalks, are then 

29 Chem. Abstracts 33 (1930), 5132. 



Courtesy of Fritzsche Brothers, Inc., New York. 

PLATE 7. Enfleurage process. (Spreading of jasmine; flowers on top of the fat layer on 
the glass plates of the chassis.) 


strewn by hand on top of the fat layer of each glass plate. Blossoms wet 
from dew or rain must never be employed, as any trace of moisture would 
turn the corps rancid. The chassis are then piled up and left in the cellars 
for 24 hr. or longer, depending upon the type of flowers. The latter rest 
in direct contact with one fat layer (the lower one), which acts as a direct 
solvent, whereas the other fat layer (beneath the glass plate of the chassis 
above) absorbs only the volatile perfume given off by the flowers. 

After 24 hr. the flowers have emitted most of their oil and start to wither, 
developing an objectionable odor. They must then be removed from the 
corps, which process, despite all efforts to introduce labor-saving devices, 
is still done by hand. The careful removal of the flowers (defleurage) is 
almost more important than charging the corps on the chassis with fresh 
flowers (enfleurage) and, therefore, the women doing this work must be 
experienced and skilled. Most of the exhausted flowers will fall from the 
fat layer on the chassis glass plate when the chassis is struck lightly against the 
working table, but since it is necessary to remove every single flower and 
every particle of the flowers, the women use tweezers for this delicate opera- 
tion. Immediately following defleurage, that is, every 24 hr., the chassis 
are recharged with fresh flowers. For this purpose the chassis are turned 
over and the fat layer, which in the previous operation formed the top (ceil- 
ing) of the small chamber, is now directly charged with flowers. In the 
case of jasmine, the entire enfleurage process lasts about 70 days; daily the 
exhausted flowers are removed and the chassis recharged with fresh ones. 

During the height of the harvest large quantities of flowers arrive every 
morning, which necessitates certain modifications in the process. Com- 
plications result from the fact that at the beginning and at the end of the 
harvest the quantities of flowers are very limited and, therefore, it is prac- 
tically impossible to charge the chassis each day of the flower harvest with 
the same amount of flowers. 

At the beginning of, and several times during, the harvest, the fat on the 
chassis is scratched over with metal combs and tiny furrows are drawn in 
order to change and increase the surface of absorption. 

At the end of the harvest the fat is relatively saturated with flower oil 
and possesses their typical fragrance. The perfumed fat must then be 
removed from the glass plates between the chassis. For this purpose it is 
scraped off with a spatula and then carefully melted and bulked in closed 
containers. The final product is called pomade (pomade de jasmin, pomade 
de tubereuse, pomade de violet, etc.), the most highly saturated pomade being 
Pomade No. 86, because the corps on the chassis has been treated with fresh 
flowers 36 times during the whole process of enfleurage. At the beginning of 
the harvest every chassis is charged with about 360 g. of fat corps on each 
side of the glass plate, in other words, with 720 g. per chassis. Every kilo- 



PLATE 8. Dcfleurage process. (Removal of jasmine flowers from the chassis.) 

gram of fat corps should be in contact with about 2.5 kg. (preferably with 
3.0 kg.) of jasmine flowers for the entire period of enfleurage, which lasts 
from 8 to 10 weeks. The quantities differ somewhat in the case of other 



At the end of the enfleurage, the fat corps has lost about 10 per cent of its 
weight because of various manipulations. In other words, the total yield 
of the fragrant Pomade No. 36 is about 10 per cent less than the fat corps 
originally applied to the chassis. Most of this loss is caused by fat adhering 
to the exhausted flowers when they are removed (defleurage) every 24 hr. 

(c) Alcoholic Extraits. In the early days of perfumery, the fragment 
pomades were employed directly ; later they were extracted with high proof 
alcohol, the alcohol dissolving the natural flower oil from the pomade. 
These alcoholic washings are called Extrait No. 36 when made from Pomade 
No. 36; they reproduce the natural flower perfume to a remarkable degree. 

FIG. 3.23. Sketch of a Battcuse for the extraction of flower concretes with alcohol. 
(The agitation is in counter-rotary motion.) 

Since no heat is applied during the process of enfleurage and during the 
washing of the pomades with alcohol, the extraits contain the natural flower 
oil as emitted by the living flowers. The only disadvantage exists possibly 
in a slight fatty "by-note" which can be eliminated to a certain extent by 
freezing and filtering the alcoholic washings. This slight fatty "by-note" 
is not always objectionable, as it imparts a certain roundness and fixation 
value to the finished perfumes, especially in conjunction with synthetic 

In order to prepare the extraits, the pomades are usually processed during 
the winter months when the factories are not busy with other work. For 
this purpose the pomades are charged into so-called batteuses (Fig. 3.23), 


closed copper vessels heavily tinned inside and equipped with strong stirrers 
around a vertical shaft. Several batteuses are arranged in batteries, the 
stirrers of each battery being driven by a powerful motor. The work, which 
goes on for several months, is carried out in cool cellars in order to prevent 
loss of alcohol by evaporation. Each batch of pomade is stirred for several 
days, the usual process of methodical extraction being applied. The alcohol 
employed in the process travels from one batch of pomade to the next 
(constituting in turn the third, second and first washings of successive 
batches), until it becomes enriched with flower oil and is drawn off as 
the alcoholic extrait. For the last washing, fresh alcohol is used, which 
also, in its turn, becomes gradually enriched by the continuous process 
just described. When extended to a fourth and fifth washing, this method 
extracts the pomades so efficiently that the exhausted fat is quite odorless. 
Being useless for new enfleurage it is usually employed for the making of soap. 

The fully circulated washing called "Extrait No. 36" is run through a 
refrigerator and cooled to well below freezing temperature, if possible to 
15, Most of the fat dissolved in the strong alcohol separates. The cold 
alcoholic solution (Extrait No. 36) is then filtered, also at low temperatures. 

The quantity of alcohol to be employed for the washing of each batch of 
pomade is calculated with a view to obtaining, finally, 1 kg. of extrait per 
kilogram of pomade. Obviously some alcohol is lost by evaporation during 
the process of stirring. 

The purified extraits reproduce the perfume of the living flowers remark- 
ably well. In fact, during the nineteenth century these extraits were widely 
employed as bases of the classical French perfumes, and several conserva- 
tive houses still continue this practice. Some of the well-known French 
perfumes undoubtedly owe their success partly to a high content of extraits. 
The washing of the pomades is carried out not only by the factories in Grasse 
but in some instances also by perfume manufacturers in Paris, London, 
Berlin and New York who possess the necessary batteuses and freezing ap- 

Since World War I, however, most perfumers have discontinued the 
cumbersome practice of processing the pomades purchased in Grasse; be- 
sides, high custom barriers prevented the shipment of alcoholic washings 
from Grasse into foreign countries. For these reasons the Grasse manufac- 
turers started to offer their extraits in a more concentrated and convenient 

(d) Absolutes of Enfleurage. As mentioned previously, an extrait con- 
tains not only the natural flower oil, but also a small quantity (about 1 
per cent) of alcohol soluble fat, dissolved from the corps, which cannot be 
eliminated, even by cooling the extrait far below 0. When concentrating 
the extrait by distilling off the alcohol, the content of natural flower oil and 


fat increases correspondingly. Complete concentration in a vacuum still 
at low temperature results in a concentrated flower oil, free from alcohol, 
the so-called absolute of enfleurage. 

The crude absolutes of enfleurage are usually of dark color and, because 
of their fat content, of a semisolid consistency. Lighter colored products 
of more liquid consistency can be obtained by certain methods of purification 
whereby more fat is eliminated. Further elimination of fat and purification 
increases the price of the final absolute. Every manufacturer has his own 
standards in this respect. 

These so-called absolutes of enfleurage, absolutes of pomade, concentrates 
of pomade or liquid concretes were widely employed before the introduction 
of the more modern process of extraction with volatile solvents. Even 
today these absolutes of enfleurage find favor with some perfumers because 
of their lower price. Experts, however, claim that the absolutes of en- 
fleurage when redissolved in alcohol are somewhat inferior to the original 
alcoholic extraits. Apparently during the process of concentration certain 
constituents of the natural flower oil, especially the most volatile and delicate 
ones, are lost. 

A characteristic of absolutes of enfleurage is that they have a slight but 
noticeable "by-note" of vanillin quite alien to the true flower perfume. 
This note originates from the minute quantities of benzoin incorporated into 
the fat corps for protection against rancidity. Soluble in alcohol, the ben- 
zoin dissolves when the pomades are extracted with alcohol and upon con- 
centration it accumulates in the absolute. 

(e) Absolutes of Chassis. When describing the process of enfleurage we 
mentioned that the flowers are removed from the fat corps on the chassis 
every 24 hr. These flowers arc not thrown away because they still contain 
that part of the natural perfume which was not absorbed by the fat. It 
must be borne in mind that the perfume or essential oil of the flowers con- 
sists not only of volatile constituents, but also of compounds of higher boil- 
ing range which are not so readily released by the flowers. The actual 
conditions are probably much more complicated and many physiological 
processes take place, which so far have not yet been fully elucidated. 

The part of the natural flower oil which is retained by the flowers after 
removal from the chassis (defleurage) can be extracted from these partly 
exhausted flowers with a volatile solvent petroleum ether, for instance. 
Concentration of the solution results in a solid mass. (This product must 
not be confused with the concretes and absolutes obtained by extracting 
fresh flowers directly with volatile solvents.) The solid mass thus obtained 
contains a certain percentage of fat originating from the corps with which 
the flowers were in contact during the process of enfleurage; it is purified and 
made alcohol soluble by eliminating most of the fats at low temperature. 


The final so-called absolute of chassis, a viscous, alcohol-soluble oil, possesses 
an odor differing somewhat from that of the absolute of enfleurage. 

Absolute of enfleurage and absolute of chassis logically supplement one 
another because each represents only part of the total natural flower oil 
present in the living flowers. Yet, they are usually marketed separately, 
perhaps because the absolute of chassis is lower priced than the absolute 
of enfleurage. 

Absolutes of chassis give excellent results in perfume blends, especially 
in conjunction with synthetic aromatics, the harsh notes of which are thereby 
softened and blended. 


As explained, certain flowers e.g., jasmine and tuberose give their 
greatest yield of flower oil upon extraction with cold fat (enfleurage) because 
their physiological activities continue for 24 hr. and longer after harvesting. 
During this period, the fat on the chassis absorbs the perfume emitted by 
these flowers. 

However, the physiological activities of other flowers roses, orange 
blossoms, acacia, and mimosa, for instance are stopped by picking. 
When extracted or distilled, they yield, therefore, only as much oil as is 
contained in the flowers at that moment. Since no further oil develops in 
these flowers, the long and rather complicated method of enfleurage would 
prove ineffective. Hence, other methods must be resorted to, whereby 
a medium actually penetrates the plant tissues and dissolves all flower oil 
present in the oil glands. 

Hesse and Zeitschel 30 studied methods of distillation, cold enfleurage, 
maceration with hot fat, and extraction with volatile solvents as applied to 
various flowers, and the effect upon the yield of flower oils. Applying 
enfleurage to orange blossoms, for instance, Hesse found that this method 
yields only one-fifteenth of the amount of volatile oil obtained by steam 
distillation. Hesse thereby confirmed what had been known empirically 
in Grasse for generations. 

Generations before the modern process of extraction with volatile sol- 
vents had been introduced (probably even in classical times), the perfumes 
of roses, orange blossoms, violets, acacia, mimosa and others had been ob- 
tained by treating the flowers with hot fat. The principle is simple : 

The flowers are extracted by immersion in hot fat. In other words, the 
same batch of hot fat is systematically treated with several batches of fresh 
flowers until the fat becomes quite saturated with flower perfume. The 
exhausted flowers are removed and the fragrant fat, called Pomade d'Orange, 
Pomade de Rose, etc., is sold as such, or the pomade may be treated further 

* J. prakt. Chem. [2], 64 (1901), 250, 258; 66 (1902), 506, 513. 


by washing it with strong alcohol, exactly as with jasmine or tuberose 
pomades, obtained by cold enfleurage. The alcoholic extraits (Extrait d 'Or- 
ange, Extrait de Rose, etc.) may be marketed as such, or they are concen- 
trated in vacuo, giving thereby the corresponding absolutes of pomade. 

The process of maceration, therefore, is somewhat analogous to that of 
enfleurage, with the fundamental differences that, in the case of maceration, 
hot fat is employed, and that the actual macerating of the flowers in the hot 
fat is done quickly. 

Maceration was an important process before the introduction of the 
more modern method of extraction with volatile solvents. Fifty years ago, 
orange blossoms, if not distilled, were treated by maceration; acacia blos- 
soms, which do not lend themselves to steam distillation, had to be processed 
exclusively by maceration. Similarly, roses were macerated in Southern 
France because French roses, unlike Bulgarian roses, give only a very low 
yield of oil upon distillation. However, today, the process of maceration 
with hot fat is employed very little. Its products, especially those from 
orange blossoms, find application only in a few old-fashioned perfume 
formulas. Otherwise the concretes and absolutes made by volatile solvent 
extraction have almost completely replaced the former extraits and absolutes 
of maceration. 

For completeness, however, we shall give a brief description of the way 
this old-fashioned process is carried out : 

As solvent a highly purified fat base is employed. It should be prepared 
most carefully and in the same way as described under enfleurage. 

A batch of 80 kg. of corps is heated to about 80 and at that temperature 
macerated with charges of 20 kg. of fresh flowers each time. This is re- 
peated until 1 kg. of corps has been treated with about 2 to 2j kg. of flowers. 
Every extraction lasts about one-half hour, at 80, when the mass is left 
standing for about an hour during which it cools but continues macerating 
the flowers. The mass is then reheated, melted and strained through metal 
sieves and filter bags, whereby the exhausted flowers are eliminated. Since 
they retain some adhering fat, they are, while in the sieves, treated with 
scalding water, which liquefies the fat. The water easily separates from the 
fat layer. In order to remove all adhering fat, the flowers are finally packed 
between filter cloth, placed in a hydraulic press and submitted to pressure 
ranging up to about 3,750 Ib. per sq. in.. Scalding water is thrown on 
the filter bags during the process so that any fat still retained by the flowers 
is melted and expressed. Expressed fat and water again separate easily. 
Instead of hydraulic presses, some manufacturers employ centrifuges for 
removing the exhausted flowers from the fat corps. 

The method of maceration is rather cumbersome but it served its pur- 
pose in the old days when no better process was available. Its products 


(extraits and absolutes of maceration) often show a fatty "by-note" which 
originates from the fat corps and modifies the character of the original flower 
perfume. A further disadvantage consists in the fact that, on account of this 
fat content, absolutes of maceration easily turn rancid, thereby developing 
a sharp, disagreeable note. Because of their high alcohol content, the 
extraits are better protected against rancidity and spoilage in general. 


This method was first applied to flowers in 1835 by Robiquet. 31 Some- 
what later Buchner, 32 and Favrot 33 experimenting independently, processed 
flowers with diethyl ether. Around 1856, Millon 34 in Algeria extracted 
flowers with various solvents; Hirzel 35 in 1874 suggested petroleum ether as 
the most suitable solvent and obtained patents for his apparatus in several 
countries of Europe. Gradually the new method attracted the attention of 
the manufacturers in Southern France (Grasse and Cannes) and large-scale 
experiments were conducted independently by several industrial workers 
such as Piver, Vincent, Roure, Naudin, Massignon, Chiris, Charabot, and 
Garnier. 36 The latter obtained a patent for a novel type of rotatory extrac- 
tor and extended his activities from Southern France to Bulgaria, Syria, 
Egypt and Reunion Island. Finally all the flower oil manufacturers in 
Grasse were forced to adopt the volatile solvent process, and constructed 
special extraction plants in addition to their existing enfleurage buildings. 

The principle of extraction with volatile solvents is simple : fresh flowers 
are charged into specially constructed extractors and extracted systemati- 
cally at room temperature, with a carefully purified solvent, usually petro- 
leum ether. The solvent penetrates the flowers and dissolves the natural 
flower perfume together with some waxes and albuminous and coloring 
matter. The solution is subsequently pumped into an evaporator and con- 
centrated at a low temperature. After the solvent is completely driven off 
in vacua, the concentrated flower oil is obtained. Thus the temperature 
applied during the entire process is kept at a minimum ; live steam, as in the 
case of distillation, does not exert its action upon the delicate constituents of 
the flower oils. Compared with distilled oils the extracted flower oils, 
therefore, more truly represent the natural perfume as originally present in 
the flowers. 

/. Pharm. 21 (1835), 335. Buchner's Repert. f. d. Pharm. 54 (1835), 249. Pharm. 
ZentraM. (1835), 553. 

82 Buchner's Repert. f. d. Pharm. 56 (1836), 382. 

83 /. Chem. med. (1838), 221. Pharm. Zentralbl. (1838), 442. 

84 /. Pharm. chim. [3] 30 (1856), 407. Compt. rend. 43 (1856), 197. 

35 "Toiletten-Chemie," 3d Ed., Leipzig (1874), 77. 

86 For details see Perfumery Essential Oil Record 12 (1921), 197-222. 


Despite this obvious advantage the volatile solvent process ca?-^>t en- 
tirely replace steam distillation, which remains the principal mtiLfcjd of 
isolating essential oils. Steam distillation, in most cases, is a simpler 
process: by employing portable direct fire stills, distillation can be carried 
out even in remote and primitive parts of the world, whereas solvent extrac- 
tion necessitates complicated and expensive apparatus, and a crew of well- 
trained workers. Running expenses arc comparatively high; a mistake in 
operation can be costly; the unavoidable loss of solvent, of which large quan- 
tities are employed during the process, is an important factor in the price 
calculation of natural flower oils. Extraction with solvents can, therefore, 
be applied advantageously only to the higher priced materials, particularly 
the flowers. A loss of 10 liters of solvent per 100 kg. of flower charge re- 
mains rather insignificant in the calculation of absolute of jasmine which is 
normally valued at several hundred dollars per pound; 37 but with low-priced 
oils such as rosemary or eucalyptus, ranging normally below SI. 00 pel 
pound, the loss of a few liters of solvent would make extraction prohibitive. 

All extracted flower oils are of more or less dark color because they con- 
tain much of the natural plant pigments which are not volatile. Steam 
distilled oils, on the other hand, are in most cases of light color. Further- 
more, they usually are soluble even in dilute alcohol, while extracted oils 
require 95 per cent alcohol for complete solution. 

Despite these drawbacks, the products of extraction possess one supreme 
advantage, i.e., their true-to-nature odor. In addition, certain types of 
flowers e.g., jasmine, tuberose, jonquil, hyacinth, acacia, mimosa and 
violet do not yield their volatile oil on steam distillation, and must, there- 
fore, be extracted with solvents. 

(a) Selection of the Solvent. The most important factor for the suc- 
cess of the extraction process is the quality of the solvent employed. The 
ideal solvent should possess several properties: 

1. It should completely and quickly dissolve all the odoriferous principles 
of the flower, yet as little as possible of such inert matter as waxes, pigments, 
albuminous compounds, otc. In other words, the solvent should be se- 

2. It should possess a sufficiently low boiling point to permit its being 
easily removed (distilled off), without resorting to higher temperatures; yet, 
the boiling point should not be too low, as this would involve considerable 
solvent loss by evaporation in the warm climate of Southern France. 

3. The solvent must not dissolve water since 'the water present in the 
flowers would dissolve and accumulate in the solvent. 

Up to $2,000.00 per Ib. in 1946. 


4. The solvent must be chemically inert, i.e., not react with the con- 
stituents of the flower oil. 

5. The solvent should have a uniform boiling point; when evaporated 
it must not leave any residue. The slightest traces of high boiling com- 
pounds, upon evaporation of the solvent, would accumulate and remain in 
the flower oil and completely spoil its odor. It should be borne in mind 
that the yield of flower oil is generally very small, and that large quantities 
of solvent are required to cover the flower material in the extractors. In 
the case of petroleum ether, for instance, even traces of high boiling im- 
purities are apt to impart to the concretes and absolutes an objectionable 
off-odor of kerosene, which cannot be eliminated without doing considerable 
harm to the delicate flower oil. 

6. The solvent should be low-priced and, if possible, nonflammable. 

The ideal solvent which would fulfill all these requirements does not 
exist. Considering every feature, highly purified petroleum ether appears 
to be the most suitable one, with benzene (benzol) ranking next. 

Mixed solvents form a fascinating problem which so far htis been little 
touched, but which promises quite interesting results. As compared with 
straight solvents, mixed solvents can either reduce or increase their dis- 
solving power. Much experimental work along these lines has still to 1x3 

Petroleum Ether. Crude petroleum on fractional distillation yields a 
number of hydrocarbon fractions of different boiling ranges which find 
certain'' industrial applications. The fractions, boiling range 30- 70, com- 
mercially called petroleum ether, consist of saturated paraffins, viz., mainly 
pentane and hexane. Because of their chemical inertness and complete 
volatility, these fractions are particularly suited for flower extraction. A 
further advantage lies in their selective power of dissolving: they yield 
products which contain relatively little wax, albuminous and coloring matter, 
but correspondingly more of the odoriferous compounds. Certain American 
petroleums are best suited for our purpose, because they consi.^t mostly of 
inert, saturated paraffins, whereas Galician, Rumanian, Russian or "cranked 
petroleum" contain derivatives of benzene and naphthene, as well as un- 
saturated olefinic compounds, the latter being chemically active and liable 
to polymerization. They may thus form high boiling compounds of ob- 
jectionable kerosene odor, especially on prolonged use of the solvent. 

The petroleum ether must be free from sulfur and nitrogenous com- 
pounds. It is purified by washing in turn with strong sulfuric acid, water, 
hot dilute sodium hydroxide solution, water, and then drying. Cas- 
tille and Henri 38 recommended repeated washing with sulfuric acid mono- 

8 Bull. we. chim, biol. 6 (1924), 299. 


hydrate, followed by washing with alkaline potassium permanganate solu- 
tion and drying. They found the hexane fraction of petroleum ether, 
boiling range 65-70, of great advantage in extraction work because solutes 
remain in their normal molecular state; unstable compounds stay un- 
changed and no addition compounds are formed. 

When testing petroleum ether for use in extraction work, special atten- 
tion must be paid to the presence (absence!) of a nonvolatile residue. For 
this purpose a sample of 50 cc. should be evaporated in a glass or porcelain 
dish at a temperature not exceeding 40. After complete evaporation the 
glass dish should show no residual odor whatsoever, but especially no odor 
indicating the presence of kerosene or sulfur compounds. A similar test 
can be carried out by permitting the solvent to evaporate on a clean filter 
paper at room temperature. More detailed methods of testing petroleum 
ether for purity are described in the "United States Pharmacopoeia," 
Thirteenth Revision. 

In the extraction plants of Southern France the petroleum ether is 
usually prepared by submitting petroleum fractions to slow and repeated 
rectification in special stills provided with high fractionation columns and 
dephlegmators. As a rule, a small quantity (about 5 per cent) of odorless 
paraffin or fat is added to the gasoline in the still so that higher boiling com- 
pounds are retained and prevented from distilling over. According to the 
quality of the gasoline employed, 20 to 40 per cent remains as residue in the 
still, while 00 to 80 per cent represents the final cceur (heart) of petroleum 
ether suitable for extraction. Its boiling point should not be higher than 75. 
Although petroleum ether is the best solvent found so far for flower ex- 
traction, it possesses some inherent disadvantages for example, relatively 
high solvent losses in the course of the extraction process. These losses are 
due primarily to evaporation of the low boiling, almost gaseous, fractions. 
Furthermore, petroleum ether is readily inflammable and dangerous to 
work with. 

Benzene (Benzol). Benzene ranks next to petroleum ether as a solvent 
for the extraction of flowers. It is a coal-tar product made by treating and 
purifying coal-tar naphtha with sulfuric acid and subsequently with sodium 
hydroxide. The fractions below 130 contain the lower benzene hydro- 
carbons which are composed mainly of benzene (CeHe), toluene, and other 
homologucs. The industrial "benzol" often contains pyridine, carbon 
disulfide and thiophene which must be removed by treatment with concen- 
trated sulfuric acid, water and caustic soda solutions. Further fractiona- 
tion eliminates most of the higher boiling homologues but complete purifica- 
tion is obtained only by repeated crystallization. Thus, pure benzene 
melting point 5.5, is obtained, the higher homologues remaining liquid and 
being separated by vacuum filtration, or other methods. 


Crystallizable benzene is of such purity that 95 to 98 per cent of it 
distills within 1 per cent of the theoretical boiling point 80.1. This uniform 
boiling point is of great advantage in extraction work, also because solvent 
losses are reduced. Yet, 80. 1 is a relatively high boiling point, which makes 
it rather difficult to remove the last traces of solvent from the concentrated 
flower oil. 

A further drawback of benzene in flower extraction work lies in its high 
dissolving power. It dissolves not only the odoriferous principles but also 
much wax, albuminous, and coloring matter, so that the final flower oils 
extracted with benzene are dark, highly viscous, often almost solid masses, 
which can be purified only under considerable difficulties and by special 

Compared with petroleum ether, benzene usually gives much higher 
yields of concretes, due to the higher amount of inert wax, albuminous, and 
coloring matter present. As far as the actual odoriferous principles are 
concerned, the yields obtained by benzene or petroleum ether are usually 
quite similar. 

Summarizing, it can be stated that petroleum ether is preferred for ex- 
tracting the more expensive flowers, while benzene serves in the case of 
lower priced plant material such as oak moss and labdanum, where the 
presence of coloring matter is not considered of too great a disadvantage. 

Alcohol. Alcohol cannot be used for the extraction of fresh flowers 
because it dissolves the water contained in them and becomes increasingly 
more dilute. With some flowers (tuberoses, for example) alcohol develops 
a most disagreeable odor; from others (jasmine, for example) it extracts 
dark, solid masses which possess an odor similar to molasses. 

High-proof alcohol in some instances dilute alcohol is widely em- 
ployed, however, for the extraction of dried plant materials, leaves, barks, 
roots, and especially gums, from which alcoholic tinctures are obtained. 
These tinctures find wide application in pharmacy and perfumery. 

Concentration of these tinctures, usually by driving off the alcohol in a 
vacuum still, results in the so-called oleoresins and resinoids. These prod- 
ucts are usually viscous, often almost solid, masses of dark color, represent- 
ing the concentrated odoriferous principles, plus the alcohol soluble resins, 
coloring matter, etc., contained in the original plant material. 

Resinoids of olibanum, myrrh, opopanax, benzoin, etc., are widely em- 
ployed in perfumery, oleoresins of vanilla, ginger root, capsicum, celery 
seed, etc., in the flavoring of all kinds of food products and beverages. 

(b) Apparatus of Extraction. 

General Arrangement. The extraction buildings of the Grasse region are 
usually of light masonry, one-storied, painted in light colors. The flat roof 
serves as a shallow water tank, insulating the building against sunheat and 


providing the condensers in the building below with water. The steam 
boilers are housed separately, at a safe distance from the main building, in 
order to exclude any danger of fire. The employment of volatile, highly 
inflammable petroleum ether or benzene also necessitates that all electric 
motors and switches be explosion proof, or be housed outside of the extrac- 
tion building. The reserve solvent which is not in circulation must be 
stored in fireproof cellars, separate from the buildings. 

The extraction building is equipped with one or two stills or columns for 
fractionating the solvent, a few batteries for extracting the flowers, and 
stills for concentrating the flower oil solutions. The batteries are of differ- 
ent size, so that they can be used according to the quantity of available 
flower material, which varies according to weather conditions and with the 
progressing harvest. 

Construction of Apparatus. Until some years ago the extractors and 
stills were constructed of copper, because this metal retains its value after 
scrapping the apparatus, and the pliable copper can be hammered and re- 
pairs are easily made. Lately, however, the extractors are constructed 
more often of heavily tinned sheet iron which is much cheaper and, there- 
fore, offers the advantage of lower investment and quicker amortization. 

The apparatus must be of solid construction to stand wear and tear ; all 
extractor pipes and valves should be within easy reach to save time and 
exclude mistakes on the part of the operators. Pipes and valves must be 
sufficiently wide to prevent formation of pressure by air and petroleum ether 
vapors, one of the principal causes for loss of the solvent in vapor phase. 
Large diameters also permit quicker flow of solvent and solutions to and 
from the apparatus, and considerably speed up operation. Pumping of 
solvents and solutes is done by air pressure created by air compressors. 

The extractors are mounted on elevated metal platforms along the inside 
walls of the building. The platform runs even with the ground outside of 
the building, so that the arriving flower material may be charged directly 
into the extractors and the exhausted flowers discharged with equal ease. 

Loss of solvent during the operation presents one of the most serious 
problems. These losses arc usually caused by incomplete distillation of the 
solvent from the exhausted flowers, by insufficient condensation in the con- 
densers, or by too narrow pipes and valves creating pressure and blowing 
off a mixture of air and solvent vapor. To avoid this as much as possible 
the whole system of extractors, evaporators and solvent tanks is arranged 
as a closed circle, with only one outlet where escaping solvent vapors can be 
condensed. The Socie*te* Carbonisation et Charbons Actifs ome years ago 
developed an efficient, rather small sized apparatus in which solvent vapors 
are absorbed by activated carbon and recovered by blowing live steam 
through the saturated carbon. A current of hot air then reactivates the 



carbon. The apparatus is simple and permits considerable economy in 
factories where large amounts of solvent are in circulation. 

Description of Extraction Batteries. A battery usually consists of three 
or four extractors, four or five metal tanks holding solvent and solutions, 
and an evaporator for concentrating the flower oil solutions. There exist 
two types of extractors viz., the stationary and the rotatory types. Some 
factories employ both, but only one type can be used in the same battery. 

The stationary extractors usually have a capacity of 1,200 liters, holding 
about 135 kg. of jasmine flowers, or 180 kg. of rose flowers. From 400 to 
450 liters of solvent are required for extracting 100 kg. of flowers. Losses 
of petroleum ether may range from 12 to 14 liters for 100 kg. of flowers 
treated, but the loss can be considerably reduced with the solvent recovery 
apparatus described above. 

Courtesy Les Parfumeriea de Seillans, (Var), France, through Fritzsche Brothers, Inc.., New York. 
PLATE 9. The extraction of jasmine flowers with volatile solvents. 

The stationary extractors are cylindrical, standing vertical. In the 
interior they should be provided with several perforated metal grids ar- 
ranged horizontally around a vertical central support shaft. The flowers 
are charged upon these grids, thus spreading loosely over a larger surface 
and preventing lumping. The solvent can thus penetrate the mass freely 
and uniformly. After the flowers have been charged into the extractor, 
the metal cover on top is closed tightly with clamps. 



Extraction is carried out methodically by successive washings whereby 
each batch of flowers is treated three times with solvent. A third washing 
is used as second washing for the next flower batch, then as first washing, 
and is finally pumped into the evaporator for concentration. The solvent 
distilled off is used as fresh solvent for a third washing which serves again as 
second of the next flower batch, etc. A fourth extraction, in most cases, 
yields at best only small quantities of waxes and other inert substances. 
r f he actual flower oil is contained in the first and second washings, while the 
third one serves merely to wash down parts of the second washing still 
adhering to the flower material. There exist, however, cases of emergency, 


* "*~ 



+ ! 









* "*" 






|. j 


- r - - - - 




Fresh or 







+ (rt 


* ~" Pump 

Fio. 3.24. Schematic diagram of an extraction system. 
(Extraction with volatile solvents.) 

especially during the height of the harvest, when great quantities of flowers 
arrive and must be worked up quicklj r in order to avoid fermentation. 
In such cases the third washing is often eliminated altogether, in order to 
save time. Just how to proceed requires experience and good judgment on 
the part of the factory manager. 

After the third washing the flowers are practically exhausted, and 
can be discharged. However, they still contain a considerable amount of 
adhering solvent which, before discharging the flowers from the extractor, 
must be recovered by steam distillation, i.e., by simply blowing live steam 
through the mass. Water and solvent, after condensation, separate auto- 
matically in a specially constructed Florentine flask. 

The first washing requires about 45 inin., the second 35 min., the third 



25 min. For drawing off the solutions and pumping in the next washing, 
5 to 10 min. must be allowed for each operation. Including 90 min. of 
steam distillation for recovering the solvent still adhering to the exhausted 
flowers, complete extraction of one batch of flowers requires about 4? to 5 hr. 
However, no strict rules can be laid down, as every flower type requires a 
different method of working, and every manufacturer follows his own ideas. 

Fig. 3.24 shows a schematic diagram of a system for extraction of flower 
material with volatile solvents. 

Rotatory Extractors. Years ago, Charles Gamier invented a rotatory 
extraction apparatus which was adopted by many factories. In modified 
and improved form 39 the apparatus represents a simple, solid and moderately 
priced piece of machinery. 

Steam Outlet 
to Condenser 

Charging and 
Discharging Ports 

>lvent Dram 

FIG. 3.25. Rotary extractor, Gamier type. 

The latest model (Fig. 3.25) consists of a heavily tinned iron drum rotat- 
ing around a horizontal axle. Four perforated metal partitions, rectangu- 
larly and horizontally arranged around the central axle, divide the interior 
into four compartments into which the flowers are charged through four 
manholes. While the whole system rotates slowly, the flower material 
moves, tumbles and dips into the solvent lying on the bottom of the extrac- 
tor. The liquid seeps through the perforations and drips back to the bottom 
when one compartment is lifted out of the solvent in the continuous move- 
ment of the whole drum. Thus, the solvent does not fill the extractor but 
only the lowest part, the flowers dipping slowly and continuously into the 
solvent and rising again in the rotatory movement. 

n French Patent No. 585199, October 30 (1923). See also Apparatus of Hugues, 
French Patent No. 508085, December 12 (1919). 


Three successive washings are usually made, carried out similarly to the 
systematic extraction method described under stationary apparatus. The 
first, i.e., the most saturated washing, is then pumped into the evaporator 
and concentrated by distilling off the solvent. After the third washing has 
been drawn off the exhausted flower material, live steam is blown into the 
extractor to distill over and recover the petroleum ether still adhering to the 
extracted flowers. 

The advantages of the rotatory extractors as compared with stationary 
apparatus are evident. Through the movement of the flower material in 
the solvent, its action becomes more penetrating and more effective, result- 
ing in a somewhat higher yield. Figured as concrete, it is about 8 per cent 
higher in the case of the rotatory apparatus. Since the solvent covers 
only the bottom of the rotating drum and not the whole flower material, 
as in the stationary apparatus, much less solvent is in circulation and, 
therefore, evaporation losses are reduced. Only 160 to 170 liters are re- 
quired in the rotatory apparatus to extract 100 kg. of flowers. The loss of 
solvent for 100 kg. of flowers is less than in stationary extractors ; it may be 
8 to 12 liters but can be reduced by using the previously described solvent 
recovery apparatus. 

One rotatory extractor does the work of three or four stationary extrac- 
tors arranged in one battery. Although superior in many ways the rotatory 
extractors suffer from several disadvantages and cannot altogether replace 
the stationary type ; for example, the latter is better adapted to voluminous 
plant material, such as lavender, which cannot be so easily charged and dis- 
charged through the manholes of the rotating drum. 

{Concentration of Solutions. The first, i.e., the most concentrated, wash- 
ing is filtered through a fine screen and pumped into the so-called evaporator 
in which the greater part of the solvent is driven (distilled) off. These 
evaporators are of varying construction, representing basically a modified 
water or steam bath. In other words, the heating is done by indirect steam 
blown into a steam jacket beneath the still. The solvent, however, should 
not be completely driven off in this operation. Most manufacturers stop 
operation when the temperature in the still (evaporator) reaches about 60, 
because any higher temperature at atmospheric pressure would be harmful 
to the delicate flower perfume. The first washing contains, of course, only a 
small percentage of flower oil. Therefore, concentrating of this washing hi 
the evaporator means driving off 90-95 per cent of the solvent. (The 
recovered solvent serves as fresh solvent for a third washing.) The con- 
centrated solution remaining in the evaporators is permitted to cool, is 
filtered, then transferred to a special, smaller vacuum still, and there com- 
pletely concentrated in vacuo. 



Final Concentration. Vacuum stills (Fig. 3.26) of small capacity (50 to 
100 liters) serve for this purpose. The final concentration represents a most 
delicate operation and requires much experience and constant attention on 
the part of the operator. The concentrating has to be done at as low a 
temperature as possible, yet any trace of solvent must be eliminated. 
Every manufacturer has his own, often secret, methods of purification. The 
completely concentrated and purified products represent the so-called floral 





FIG. 3.26. Vacuum still for the final concentration of natural flower oils 
(removal of last traces of solvent). 

concretes, which contain the odoriferous principles of the natural flower 
perfume, plus a considerable amount of plant waxes, albuminous material 
and color pigments. The concretes are, therefore, usually of solid consist- 
ency and only partly soluble in 95 per cent alcohol. 

Concrete Flower Oils. Although these insoluble concretes are more diffi- 
cult to work with, some perfumers prefer them to the alcohol soluble ab- 
solutes, which are obtained by precipitating and eliminating the insoluble 
waxes with strong alcohol, and concentrating the filtered alcoholic solutions. 
Distilling off the alcohol from the solutions when making these absolutes 
undoubtedly entails the loss of some of the most volatile and delicate con- 
stituents of the natural flower oil. It is often claimed that an alcoholic 
washing of a concrete is superior and more true to nature than a simple 
alcoholic solution of the corresponding absolute. On the other hand, the 
processing of concretes requires special equipment and considerable time; 
' therefore, the absolutes represent a more convenient form of flower oils than 
the concretes. 


Courte*v 1> Par/umm'es de Seillans, (Far), France, through FriUsrhe Brothers, Inc., New For*. 

PLATE 10. Vacuum still for the concentration of the alcoholic washings in the preparation 

of flower oil absolutes. 

Conversion of Concretes intp Absolutes. The alcohol soluble absolutes 
are prepared from the concretes by the following general method: 

The concrete is either thoroughly rubbed down in a large mortar with a 
quantity of high-proo* a- Hoi or, as some ma .ufacturers prefer, melted and 


dissolved in warm alcohol. Subsequently eight to ten times the amount of 
alcohol is added and the mass stirred for a prolonged period in batteuses, 
as described under enfleurage. Usually five to six washings of the concrete 
are made in a systematic way, i.e., a third washing serves as a second one for 
a following batch of concrete ; the second is used as first for a batch of new 
concrete, the first washing consequently representing the most concentrated 
solution. After standing and drawing off the clear solution from the alcohol 
insoluble waxes, the first washing is then thoroughly cooled in a refrigerator 
or in a special room, at temperatures ranging from 20 to 25, when 
more wax precipitates and is filtered off in the cold. The resulting clear 
solution can be used as such in alcoholic perfumes. 

Most perfume houses have neither the time nor the facilities to carry 
out their own washing of concretes, and prefer using alcohol soluble floral 
oils. For those, the manufacturers in Grasse offer the so-called liquid 
absolutes as the most concentrated and convenient form of floral oils. These 
liquid absolutes of extraction are obtained by carefully concentrating the 
first alcoholic washing of the corresponding concrete at low temperature in a 
good vacuum still. This process of concentrating involves a loss of several 
liters of alcohol per kilogram of absolute. 

The absolutes are usually viscous oils with a more or less pronounced 
color, according to the degree of final purification (for which each manufac- 
turer employs his own process). The absolutes are soluble in high-proof 
alcohol, and represent the most concentrated form of natural flower oils 
used in practical perfume work. However, they must not be contused 
with the actual volatile flower oil in the scientific sense. The absolutes 
usually contain from 50 to 80 per cent of alcohol soluble waxes, and only 20 
to 25 per cent volatile oil, which can be isolated from the absolute by steam 
distillation. However, these volatile oils from the absolutes are not offered 
on the market because of their excessively high price, and because they com- 
pletely lack the high fixation value of an absolute, which is due to the 
presence of alcohol soluble natural waxes, etc., in the absolute. 


It might be worthwhile to review briefly the advantages and disadvan- 
tages of the various methods of manufacturing natural flower oils. 

1. Steam Distillation of flowers yields volatile oils for example oil of 
neroli bigarade, rose, ylang ylang. Not all types of flowers, however, can 
be processed by hydrodistillation, because boiling wr,ter and steam have a 
deteriorating influence upon the rather delicate odoriferous constituents. 
The flowers of certain plants yield no oil at all when distilled, and hence must 
be processed by methods other than distillation. 


2. Enfleurage (extraction with cold fat). This method is carried out 
only in France, where it is still practiced, but on a much smaller scale than 
in former years. The method is restricted to those flowers (jasmine, tu- 
berose, and a few others) which, after picking, continue their plant physio- 
logical activities in forming and emitting perfume. Enfleurage, in these 
cases, gives a much greater yield of flower oil than other' methods. Despite 
tliis advantage, enfleurage has lately been replaced by extraction with vola- 
tile solvents because enfleurage is a very delicate and lengthy process, re- 
quiring much experience and labor. 

3. Maceration (extraction with hot fat). This process used to be ap- 
plied to those flowers which gave a very small yield by distillation or by 
enfleurage. Maceration, however, has lately been almost entirely superseded 
by the modern process of extraction with volatile solvents. 

4. Volatile Solvent Process. Of general application, this process is today 
applied to many types of flowers, and carried out in several countries. It 
is technically the most advanced process, yielding concretes and alcohol 
soluble absolutes, the odor of which truly represents the natural flower oil 
as it occurs in the living flowers, or in the plants. 


Y. R. Naves, "Extraktion von Duftstoffen mittels fliichtiger Losungsmittel," 
Riechstoff Ind. (1936), 135, 151, 176, 212; (1937), 23, 50, 137. 

Y. R. Naves and G. Mazuyer, "Parfums Naturels," Paris, 1939. (English 
translation, ''Natural Perfume Materials," N. Y. Reinhold, 1947. Translated 
by E. Sagarin). 

(c) The Evaluation of Natural Flower Oils and Resinoids. The assay 
of distilled volatile oils .has made remarkable progress during the last 
fifty years, probably because such oils are employed in much larger quanti- 
ties than natural flower oils obtained by extraction with volatile solvents 
or by enjleurage. Moreover, the pharmaceutical profession, which uses 
many volatile oils, has always endeavored to assay carefully any products 
employed as medicine. Yet, it seems strange that so little attention should 
have been paid to the assay of such highly priced products as extracted flower 
oils, especially since it is common knowledge that sophistication of concretes 
and absolutes has become quite frequent, causing considerable loss to the 
often too credulous buyers. The reason for this neglect may be sought hi 
the unfamiliarity of many users with these highly priced yet somewhat 
ambiguous products, the quality of which may depend upon many factors 
methods of manufacturing, solvents used, degree of concentration, care in 
purification, etc. No wonder then that definite norms of quality do not 
yet exist and that the manufacturer may offer various explanations for 
deviations in his products. Indeed, some manufacturers market their 


natural flower oils in several grades, according to different degrees of dilu- 
tion, in order to suit the usage and the purse of the users. Too, they claim 
that such "standardization" will guarantee a uniformity every year which 
nature alone does not achieve. "Les arts perfectionnent la nature," to 
quote an inscription on an old fountain in Grasse. 

Natural flower oils, therefore, have remained strictly articles of con- 
fidence, and the examination of them is usually carried out by simple ol- 
factory tests. Even such tests, however, require an intimate knowledge 
of the subject, a well-trained sense of smell, and familiarity with manu- 
facturing methods and possible variations in quality, which very few buyers 
or even perfumers possess. Furthermore, any olfactory test should be 
based upon the comparison of an offered sample with standard samples of 
unquestioned purity and, if possible, of the same age. (Such samples, 
unfortunately, are seldom on hand.) It is surprising how the odor character 
of a natural flower oil may change during the first six months or year after 
its manufacture. Some odors improve for a certain period, and then slowly 
deteriorate, assuming a somewhat sour or rancid note. Something of a 
parallel may be drawn with wines of young and older vintage. In view of 
these facts, it seems highly desirable and timely to establish definite and 
universal standard methods for the physicochemical assay of natural 
flower oils and resinoids from gums, balsams, and similar plant material. 

The adaptation of routine methods as applied to distilled volatile oils 
cannot per se be extended to extracted flower oils or resinoids, as these 
products contain large proportions of natural substances which, although 
olfactorily inert, possess a variety of chemical functions which would make 
the interpretation of the analysis most difficult, if not outright impossible. 
Logically, any physicochemical assay should, therefore, be applied mainly 
to the odoriferous portions of the extracted flower oils, which are usually 
identical with the volatile fraction. In other words, the extracted floral 
oil is steam distilled and the separated volatile portion examined by the 
usual tests for specific gravity, optical rotation, refractive index, acid num- 
ber, ester number, ester number after acetylation, content of aldehydes, 
ketones, phenols, etc. 

Separation of the two portions by dry distillation at reduced pressure is 
inadvisable, because of the tendency toward pronounced and often de- 
structive pyrolysis of the higher boiling constituents. Consequently, the 
method of distillation with steam suggests itself for the separation of vola- 
tile and nonvolatile portions. 

The first attempts toward establishing such a standard method were 
made by Walbaum and Rosenthal 40 who described an apparatus for the 

40 Ber. Schimmel & Co., Jubilaums Ausgabe (1929), 189. 


determination of the content in products distillable with steam from con- 
crete and absolute flower oils. However, the separation of the volatile 
constituents from the waxes in this apparatus remains incomplete, even 
after 5 hr. of distillation, and gives much trouble, such as frothing, etc. 
Furthermore, live steam at atmospheric pressure causes hydrolysis and other 
chemical reactions. The method, therefore, can at best give only compara- 
tive results as far as the yield of volatile constituents is concerned, and only 
if carried out under absolutely unvarying and most carefully controlled 

Several years later, Naves 41 suggested a more reliable, accurate and 
practical method, using distillation with superheated steam under reduced 
pressure. When superheated, dry steam behaves like a gas, follows the gas 
laws, and in the condensate yields a higher ratio of volatile aromatic con- 
stituents to carrier steam. Acting solely by its volumetric effect, dry, super- 
heated steam is chemically less active than wet steam. Thus, with super- 
heated steam it becomes possible to distill delicate esters and other com- 
pounds which would undergo hydrolysis with wet steam at the temperature 
of boiling water. For details of the method and a description of a cleverly 
constructed apparatus, the reader is referred to an interesting paper by 
Naves, Sabetay and Palfray, 42 who also examined a number of flower oils 
for their content of volatile constituents, and recorded the physicochemical 
properties of the distillable portions. The data given, however, are not 
yet complete enough to establish reliable standards universally adaptable 
by the trade. Much work along these lines must yet be done, and many more 
samples of unquestionable purity will still have to be examined before the 
essential oil industry can agree on definite norms. 

Further progress in the perfection of the assay of natural flower oils was 
achieved by Sabetay, 43 who suggested that concretes and absolutes should 
be examined for their content of volatile constituents by codistilling these 
floral products or resinoids, etc., with ethylene glycol in a partial vacuum. 
(The same author 41 also suggested applying this method to the determina- 
tion of volatile oils in drugs and spices.) Ethylene glycol is a more efficient 
carrier than steam, and the waxes or residues remaining in the distilling 
flask will be practically devoid of any odoriferous compounds. The applica- 
tion of a partial vacuum reduces the distillation temperature to a degree not 
harmful to the delicate constituents of the floral oils. Sabetay's method 
possesses the added advantage of simplicity: 

41 Documentation scientifique No. 50, December (1936), 303. Chem. Abstracts 31 
(1937), 4772. 

42 Perfumery Essential Oil Record 28 (1937), 331. 

43 Ann. chim. anal. chim. appl. 21 (1939), 173. Chem. Abstracts 34 (1940), 3018. 

44 Ibid. 22 (1940), 217. Chem. Abstracts 35 (1941), 4547. 


If a concrete or absolute is mixed with glycol and distilled under 8-15 
mm. pressure at a temperature of 90-100, all of the volatile oil contained 
in the concrete or absolute can be driven over, separated and measured. 
For instance, weigh 1-10 g. of the concrete or absolute, add 25 cc. of ethylene 
glycol and distill at 90-100, from a 50-100 cc. Claisen flask with Vigreux 
points, fitted with a thermometer, capillary tube and receiver, and with a 
metallic or oil bath as a source of heat. As a rule, the residue in the flask 
will have little odor, but, if necessary, 20 cc. more of ethylene glycol can be 
added, and the distillation repeated a second and, possibly, a third time, 
until the distillate no longer becomes turbid upon addition of water. The 
combined distillate is diluted with water (or brine), treated with sodium 
chloride (if brine is not used) and extracted with three 20 cc. portions of a 
mixture of equal parts of pentane and ether. Dry the combined ether-pen- 
tane extracts over anhydrous sodium sulfate, remove most of the solvent 
by distillation, rinse the residue with pentane into a small Claisen flask with 
Vigreux points fitted with a capillary tube, and heat gently under 50-100 
mm. pressure to constant weight. The volatile oil thus obtained may then 
be subjected to the usual physicochemical tests. 

By comparing the figures (yield of volatile oil from the absolute or con- 
crete or resinoid, specific gravity, optical rotation, refractive index, acid and 
saponification number of the volatile oil) thus obtained with those of ab- 
solutely genuine products, conclusions can be drawn as to the purity of the 
flower oil sample investigated. 

The method of Sabetay may have to be modified in certain respects, and 
will have to be applied to numerous lots of unquestionably pure natural 
flower oils before definite standards can be agreed upon by the trade. 
Naves 45 prefers the use of superheated steam for the isolation of the volatile 
constituents from natural flower oils rather than codistillation with glycol, 
as certain constituents are relatively soluble in glycol-water solution. 

Before concluding this chapter it might be well to discuss briefly the 
interpretation of analytical results, as well as the deterioration and possible 
adulteration of natural flower oils. 

If absolutely pure, and manufactured according to unvarying methods, 
and from flowers grown in the same geographical location, natural flower 
oils should be of similar character and show little variation, especially in 
regard to their content of volatile (distillable) portions, and to the physico- 
chemical properties of the volatile constituents. This, however, is not 
always the case, particularly with enfleurage products. The care exercised 
in the manufacturing process, and especially in the final purification of the 

Chim. Ada 27 (1944), 1103, 1108. Soap, Perfumery, Cosmetics 29, No. 1 
(1946), 38. 


product, exerts considerable influence upon its quality. The latter depends 
primarily upon the ratio between the weight of flowers treated during the 
entire enfleurage season and the weight of fatty vehicle (corps) employed. 
Thus a jasmine pomade will contain more volatile constituents and possess 
a much stronger odor if 1 kg. of natural corps has been treated during the 
flowering season with 2.5 or 3.0 kg. of jasmine flowers rather than only 1.5 
kg. of flowers. Concretes obtained by extracting the flowers three times 
with solvent, instead of only twice, will contain more waxes. An absolute 
obtained by extracting the concrete four or five times with alcohol, instead 
of only three times, will contain more alcohol soluble waxes and other inert 
material, and correspondingly less volatile, odoriferous material. 

Concretes and absolutes usually acquire a reddish color upon aging. 
This color alteration, noticeable particularly in jasmine and orange flower 
extracts, may be attributed mainly to the presence of indole. The odor 
improves, usually, for a few r months, and assumes a harmonious fullness and 
depth lacking in the freshly extracted product. After a year or two of 
stability, depending of course upon proper storage, the product deteriorates 
gradually, finally acquiring a somewhat acid, rancid note, which is caused 
by the formation of acetic acid and ethyl acetate. This holds true especially 
if the product originally contained a small percentage of ethyl alcohol which 
was not removed during the final concentration. Hence, it is advisable to 
examine the aqueous phase of the analytical distillate, after extraction with 
ether, for its acid and ester number. 

Pomades and absolutes of enfleurage are particularly susceptible to ran- 
cidity and development of acidity. In fact, even the freshly prepared ab- 
solutes of enfleurage show a relatively high acid number (which should not 
exceed 80), but this is caused by the presence of alcohol soluble free fatty 
acids extracted from the fat corps. 

Adulteration of natural flower oils can be carried out in different ways, 
viz., by substitution with natural flower oils from lower priced geographical 
sources, by addition of volatile oils, or fractions therefrom, aromatic isolates 
or synthetic aromatics, or by dilution with inert materials. Thus, an ab- 
solute of jasmine marketed under the label of the Grasse region may con- 
tain the Egyptian product, a misrepresentation which, at present, can be 
detected only by olfactory tests, as we do not yet possess sufficient analytical 
data to differentiate between the products from these two geographical 
sources. The addition, to concretes, of exhausted natural flower waxes, 
obtained as alcohol insoluble residues in the preparation of alcohol soluble 
absolutes, results in a correspondingly lowered content of distillable volatile 
portions of the concrete. This can be proved by the above described distil- 
lation tests. Determination of the congealing point of the concrete may 
also give valuable hints in this respect. 


A dangerous form of adulteration consists in the addition, to concretes 
or absolutes, of both odorless matters such as exhausted waxes, fats or fatty 
oils, and volatile, odoriferous compounds which occur also in the genuine 
flower oil, but which can be obtained synthetically or by isolation from lower 
priced essential oils. Thus benzyl acetate, benzyl alcohol, indole, etc., may 
be added to jasmine absolute; phenylethyl alcohol, rhodinol, etc., to rose 
absolute; linalool, linalool acetate, methyl anthranilute, etc., to orange 
flower absolute. If cleverly carried out by properly balancing the ratio 
between odorless nondistillable and odoriferous distillable compounds, such 
sophistication may give considerable trouble to the analyst, who will have to 
depend upon olfactory tests and that, as pointed out, requires a highly 
trained and experienced sense of smell. Occasionally, natural flower oils 
are adulterated with odorless solvents such as diethyl phthalate, specific 
tests for which will be found in the chapter on "Examination and Analysis 
of Essential Oils, Synthetics, and Isolates." 

When evaluating any natural flower oil, it is always advisable to test 
first for solvents and for alcohol. Traces of alcohol should not be objec- 
tionable as they are difficult to remove in the final purification during the 
manufacturing process without impairing the quality of the product. 
However, a flower oil should never contain any solvents like petroleum ether, 
benzene, or, particularly, kerosene, because their presence indicates incom- 
plete purification ; they impart to the product an off-note most detrimental 
to the delicate odor of natural flower oils. Special tests for alcohol and 
petroleum ether are described in Chapter 4 on "Examination and Analysis of 
Essential Oils, Synthetics, and Isolates." 


The indexes of refraction of some perfumery concretes: 

Chas. L. Palfray, Ann. Mm. anal. 28 (1946), 94. Chem. Abstracts 40 (1946), 


Most essential oils consist of mixtures of hydrocarbons (terpenes, sesqui- 
terpenes, etc.), oxygenated compounds (alcohols, esters, ethers, aldehydes, 
ketones, lactones, phenols, phenol ethers, etc.), and a small percentage of 
viscid or solid nonvolatile residues (paraffins, waxes, etc.). Of these the 
oxygenated compounds are the principal odor carriers, although the ter- 
penes and sesquiterpenes, too, contribute in some degree to the total odor 
and flavor value of the oil.* The oxygenated substances possess the added 
advantage of better solubility in ^dilute alcohol and, ^mh the exception of 
some aldehydes, of greater stability against oxidizing and resinifying influ- 


ences. DUG to their unsaturated character, the terpenes and sesquiterpenes 
oxidize and resinify easily under the influence of air and light or under im- 
proper storing conditions which means spoilage of odor and flavor, and 
lowering of the solubility in alcohol. 

For many years, therefore, it has been the endeavor of the essential 
oil industry to supply the users with concentrated, terpeneless and sesqui- 
terpeneless oils. Such oils consist mainly of oxygenated compounds; they 
are more soluble, more stable, and much stronger in odor, yet retain most 
of the odor and flavor characteristics of the original oil. 

The degree of concentration is automatically limited by the amount of 
oxygenated compounds present in the natural oil. For example, an orange 
oil containing only 2 per cent of oxygenated constituents and 98 per cent 
of terpenes, sesquiterpenes and waxes can, theoretically, be concentrated 
fifty times at the most, whereas a bergamot oil containing 50 per cent esters, 
alcohols, lactones, etc., and 50 per cent hydrocarbons can be concentrated 
only to double strength. 

Before discussing in more detail the methods of manufacturing these 
concent rated, torpcnclcss and sesquiterpenoless oils, we should point out 
for clarity's sake that they must not be confused with the so-called isolates 
or aromatic isolates, or commonly but incorrectly called "synthetics" which 
are isolated from certain essential oils. For instance, citral can be isolated 
by fractionation or by chemical means from lemongrass oil, eugenol from 
clove oil, safrol from sassafras oil or camphor oil fractions, citronellal from 
citronella oil. These isolates may be converted chemically into other com- 
pounds, real synthetics, viz., citral into ionones, eugenol into vanillin, safrol 
into holiotropin, citronellal into citronellol, citronellyl acetate, hydroxy- 
citronellal or synthetic menthol. Terpeneless and sosquiterpojieloss oils 
have nothing to do with these isolates as the latter consist usually of only 
one well defined chemical substance, while the former are composed of 
several, often many, oxygenated compounds as present in the normal es- 
sential oil. 

Because of the different composition, the deterpcnation of each essential 
oil requires a special process. The general method is based upon two prin- 
ciples : (a) removal of the terpenes, sesquiterpenes and paraffins by fractional 
distillation in vacuo or (b) by extraction of the more soluble oxygenated 
compounds with dilute alcohol or other solvents. In many cases, especially 
with citrus oils, a combination of the two methods may be employed. 

The commercial term "sesquiterpeneless" oils conventionally includes 
also the terpeneless oils. In some cases, especially when the content of 
sesquiterpenes in the natural oil is small, the two terms are employed syn- 
onymously. The trade designations and^ the ndmes of the many brands on 
the market, howevtr, are not always correct from the scientific point of view. 


It would be more appropriate to name these products "Concentrated Oils," 
"Terpeneless Oils," and "Terpeneless and Sesquiterpeneless Oils." 

"Concentrated oils" are those from which only a part of the hydrocar- 
bons have been removed. This can be done by simple fractional distillation 
in vacuo. According to the process applied and the intended concentration, 
a wide range of concentrated oils, with different properties, may be obtained. 
Thus, we speak of a twofold lemon or orange oil, a fivefold oil, etc. "Ter- 
peneless oils" are those from which all or most of the terpenes and waxes 
have been removed, usually by fractional distillation. "Terpeneless and 
Sesquiterpeneless oils" are those from which the terpenes, the sesquiterpenes 
and the waxes have been eliminated. The common manufacturing practice 
is to distill off in vacuo first the terpenes, and then to extract the terpeneless 
oil with dilute alcohol, or other solvents, whereby the sesquiterpenes and 
waxes are eliminated ; or, the sesquiterpenes and waxes may be removed by 
further fractionation of the terpeneless oil in vacuo. The resulting terpene- 
less and Sesquiterpeneless oil represents the highest possible concentration 
of a natural essential oil. 

The manufacture of these products requires that the operator be well 
acquainted with the chemical composition, especially with the boiling 
ranges of the various terpenes, sesquiterpenes and oxygenated compounds 
occurring in the natural oil which he expects to concentrate. The boiling 
range of terpenes varies in most cases from 150 to 180 at atmospheric 
pressure; that of sesquiterpenes from 240 to 280. The boiling points of 
most oxygenated compounds (terpene alcohols, aldehydes, esters, etc.; lie 
between those of the terpenes and sesquiterpenes. Phenols, phenol ethers, 
and a few aromatic aldehydes form an exception, also the sesquiterpene 
alcohols, esters, etc., their boiling range falling into that of the sesquiter- 
penes or above. 

As far as solubility in dilute alcohol is concerned, the terpenes are, in 
general, only sparingly soluble, the paraffins and sesquiterpenes practically 
insoluble. The oxygenated compounds, on the other hand, possess in 
general much better solubility : the alcohols, aldehydes, ketones, and phenols 
are most soluble, the esters and phenol ethers somewhat less soluble. 

As pointed out, the terpenes may be removed by fractional distillation of 
the natural oil under reduced pressure. Most constituents of essential 
oils being deleteriously affected by heat, the distillation temperature must 
be kept as low as possible, which can be achieved with the aid of a good 
vacuum. For best results a well-constructed fractionation still as described 
in the section on "Distillation of Essential Oils" should be employed. It 
must be equipped with an efficient fractionation column. 

It should be borne in mind that the terpenes cannot be removed quanti- 
tatively from a natural oil by mere fractional distillation ; indeed, one of the 


greatest disadvantages of fractional distillation lies in the incomplete sepa- 
ration of the constituents, especially if their boiling points lie close together. 
A typical example is lemon oil which, aside from citral, contains also lower 
boiling aldehydes, such as octyl, nonyl and decyl aldehyde. If natural 
lemon oil is fractionated at 2 mm. pressure, the lower boiling terpenes should 
come over first, and theoretically the terpene fraction should contain no 
citral. However, even with a very efficient fractionation column, the alde- 
hyde content of the terpene fraction will amount to about 1.0 per cent. 
The terpene fraction may be refractionated, but it will still retain small 
quantities of aldehydes; furthermore, repeated heating affects the flavor. 
Separation of the oxygenated compounds by chemical means is limited to 
certain cases only. 

Repeated fractionation results in several intermediary fractions which 
consist of terpenes and a slight amount of oxygenated compounds, the latter 
increasing in proportion as the distillation temperature rises. Fractiona- 
tion may be conducted in such a way that the residual oil is free from ter- 
penes, but in this case the residual oil will be deprived also of those portions 
of the oxygenated constituents which have been carried over into the inter- 
mediary fractions. In order to recover these compounds, it will be neces- 
sary to refractionate the intermediary fractions, but, as said, prolonged 
heating is likely to have a deleterious effect upon the odor and especially the 
flavor of the fractions. Fractionation may be controlled by testing each 
fraction for solubility and for its rotatory power. 

The elimination of the sesquiterpenes presents even more difficulties 
than that of the terpenes. In some cases the sesquiterpenes may be sepa- 
rated from the terpeneless oils by mere fractionation in vacuo, provided that 
the oils are not affected by the relatively high boiling temperature required 
for the distillation of scsquiterpenes (about 120-140 at 10 mm. pressure) 
and by the partial overheating in the still which easily takes place. A 
vacuum of 3 to 5 mm. is desirable. In this case, too, the manufacturer must 
be familiar with the boiling points, at reduced pressure, of the various oil 
constituents. In some cases the differential in the boiling points of two 
compounds, as prevailing at atmospheric pressure, does not remain constant 
at reduced pressures ; it may even be reversed. Too, every fraction should 
be tested for its rotatory power and for solubility in dilute alcohol, the in- 
soluble ones to be rejected as containing mainly sesquiterpenes. Refrac- 
tionation of the rejected fractions may be necessary. Even at a pressure of 
only 1 mm., a relatively high temperature is required to distill over the 
oxygenated compounds, most of them boiling between 90-110. More- 
over, the temperature in the still itself will usually be about 10 and even 
20 higher than the boiling point of the liquid, and intense local heating 
occurs especially along the walls of the still. All these factors tend to im- 


part to the oil a note which the expert easily recognizes as "distilled" or 
slightly "burnt," as it does not occur in natural cold-pressed citrus oils, 
for example. Furthermore, the influence of heat seems to decompose the 
so-called "molecular compounds" which some authorities assume to occur 
in natural oils. It is a well-known fact that, upon aging, the odor of a per- 
fume or flavor mixture changes and improves considerably. This may be 
caused by chemical reactions of functional groups for example, by the 
interaction of alcohols and aldehydes which form acetals. Such compounds 
may exist in the natural oil and be decomposed upon heating and distilling. 

Another method of removing the high boiling sesquiterpenes and waxes 
from the terpeneless oil consists in steam distilling the terpeneless oil at 
reduced pressure. This process is more gentle than dry distillation in vacua 
and leaves the high boiling sesquiterpenes anc! waxes as residues in the still. 
In this case the distillate should be tested for solubility; any sesquiterpenes 
distilled over may be removed by treating the fractions with dilute alcohol. 
This method, however, has the inherent disadvantage that compared with 
dry vacuum distillation it takes much longer, especially in the case of oils 
containing a large percentage of high boiling compounds. Also, certain 
constituents of an oil are liable to dissolve in the distillation water e.g., 
phenylethyl alcohol or eugenol. In this case the distillation water has to 
be returned into the still for cohobation. 

In view of these inadequacies, some manufacturers remove all remain- 
ing terpenes and sesquiterpenes from concentrated oil by extracting the 
latter with dilute alcohol. The strength of the alcohol to be employed for 
this purpose depends primarily upon the solubility of the oxygenated com- 
pounds. Thus, the concentrated oil from which most of the torpenes and 
sesquiterpenes have been eliminated by fractionation in vacua or by steam 
distillation under reduced pressure is shaken for some time with fifteen to 
twenty times its volume of dilute alcohol, for instance, with 60 per cent 
alcohol by volume ; or the concentrated oil is first dissolved in the correspond- 
ing volume of strong alcohol and then the required amount of distilled water 
is gradually added with continuous stirring until the desired degree of alcohol 
dilution is reached. In both cases the turbid mixture should be cooled for 
a prolonged period and set aside until clarified. Thus, the oxygenated 
constituents dissolve in the dilute alcohol, while the terpenes and sesqui- 
terpenes remain undissolved and (together with traces of oxygenated com- 
pounds) may be separated. 

Because of the small differential in the specific gravity of the undissolved 
parts of the oil and that of the solution, emulsions may form and the separa- 
tion of the two layers may require some time. In order to break the emul- 
sion, small quantities of low boiling petrol ether are added, or the emulsion 
may be separated by centrif uging. The undissolved oil is repeatedly treated 


with dilute alcohol in order to extract any quantities of oxygenated com- 
pounds which it might still retain. 

The clear solution of oxygenated compounds in dilute alcohol is then 
transferred into a still and the alcohol fractionated off at reduced pressure, 
until only oil and water remain in the still. The two layers of oil and water 
can easily be separated. The employment of an efficient condenser will pre- 
vent losses of alcohol. The recovered alcohol and the residual water may 
be used again for treating the next batch of oil. 

The literature on essential oils contains many references to the pre- 
paring of terpeneless and sesquiterpeneless oils, one of the most compre- 
hensive ones being the paper by Littlejohn. 46 As stated, no standard method 
has been adopted yet and every manufacturer uses his own process. 
Romeo 47 reported that terpeneless and sesquitcrpeneless citrus oils are manu- 
factured in Sicily by first removing the terpenes by fractional distillation. 
The sesquiterpenes are then eliminated from the terpeneless oil by extracting 
the oil with dilute alcohol, the strength of which should be somewhat lower 
than that in which the sesquiterpeneless oils must finally be soluble. The 
sesquiterpeneless oil is separated from the alcoholic solution by the addition 
of water or by distilling off the alcohol under reduced pressure. This 
constitutes the general method described previously and with some modifi- 
cations it forms, today, the basis of most commercial processes. 

A more novel method has been described and patented by van Dijck 
and Ruys. 48 In this process the natural oil is extracted by two solvents 
which are only partially soluble in one another for instance, pentane and 
dilute methyl alcohol. The two solvents are made to flow, according to the 
countercurrent principle, through a horizontal glass cylinder and the oil is 
entered in the middle. The terpenes dissolve in the pentane phase, the 
oxygenated compounds in the methylalcohol phase. After separation of the 
two phases, the solvents are removed by distillation, only low temperatures 
being necessary. This, according to the inventors, is the principal ad- 
vantage of thoir method, aside from the fact that high-grade terpeneless oils 
are obtained in almost quantitative yield. The principal difficulties of this 
process lie in the necessity of working with large volumes of solvents, fur- 
thermore, in the tendency toward formation of emulsions which, however, 
might be broken in some cases by the addition of 0.1 per cent of citric or 
tartaric acid. 

After having discussed the various methods of manufacturing terpeneless 
and sesquiterpenoless oils, it might be advisable to add a few words about 

* Flavours 3, No. 4, August (1940), 7. 

47 La deterpenazione delk essenze di agrumi. Estr. dagli Atti del H. Congresso Nazionak 
di Chimica pura ed applicata. Palermo, May (1926). Ber. Schimmel & Co. (1928), 38. 
Perfumery Essential Oil Record 28 (1937), 91. 


their concentration, as there exists a great deal of confusion regarding this 
point. The price lists and tables on the concentration of terpeneless and 
sesquiterpeneless oils issued by the various essential oil houses differ widely 
in regard to their concentration value. Yet, the theoretical concentration 
could be calculated only from the actual yield of terpeneless or sesquiterpene- 
less oil as obtained from a given weight of natural oil. However, the 
actual odor and flavor strength of two oils, although of the same theoretical 
concentration, may differ, concentration not being necessarily proportionate 
to odor and flavor strength. Let us assume, for instance, that 100 kg. of 
natural lemon oil are converted into terpeneless oil and that the yield is 8 
kg. of terpeneless oil containing about 40 to 45 per cent of citral. (Some 
citral has been destroyed by distillation and, besides, the oxygenated com- 
pounds cannot be completely freed of terpenes.) In this case the actual 
concentration of the oil, but not necessarily of the flavor, is obviously 
twelve and one-half times. 

It is difficult, if not impossible, to indicate general and definite limits for 
the physicochemical properties of concentrated, terpeneless and sesquiter- 
peneless oils because of the fact that these properties depend upon the degree 
of concentration and upon the relative proportions of oxygenated consti- 
tuents originally present. Furthermore, every manufacturer has his own 
standards which are based upon his particular manufacturing process. 

Littlejohn 49 listed the physicochemical properties of more than fifty 
terpeneless and sesquiterpeneless oils. Accordinging to this author, the 
specific gravity affords a valuable clue to the presence of any remaining 
terpenes. These hydrocarbons possess a low specific gravity and refractive 
index and their complete removal should raise the specific gravity and re- 
fractive index of the terpeneless oil relative to that of the original oil. The 
determination of the optical rotation, too, provides a good indication regard- 
ing the extent to which the terpenes have been eliminated. 

By far the most important criterion for a terpeneless and sesquiterpene- 
less oil is its solubility in dilute alcohol, 70 per cent ethyl alcohol usually 
being employed for this purpose. A terpeneless oil should usually be soluble 
in 3 to 10 volumes of 70 per cent alcohol, while a sesquiterpeneless oil should 
be more soluble. 

Aside from the determination of the physicochemical properties, it is 
advisable to test a terpeneless or sesquiterpeneless oil also for its content of 
oxygenated compounds, especially for alcohols, esters and aldehydes, which 
can be done by the usual analytical methods. Bocker 60 suggested a method 
of evaluating and examining terpeneless lemon oils which is based on treat- 
ing the aldehyde-free oil with 51 per cent alcohol to remove all oxygenated 

49 Flavours 3, No. 4, August (1940), 7. 

60 /. prakt. Chem. [2], 89 (1914), 199; [2], 90 (1914), 393. 


compounds, and on measuring the quantity of terpenes and sesquiterpenes 
left. For this purpose, 10 cc. of the oil is first treated with a solution of 
neutral sodium sulfite which removes the aldehydes. The remaining, un- 
absorbed oil is shaken with 100 times its volume of 51 per cent alcohol in a 
separatory funnel, cooled to about 2 and left for a period of 6 hr. or more, 
until the liquids have completely separated when the lower layer can be re- 
moved. After washing the oil layer with a further quantity of 51 per cent 
alcohol, all undissolved oil is transferred to a burette tube and its volume 
carefully measured. From this amount the percentage of nonoxygenated 
constituents of the original oil can be determined. In order to obtain more 
exact results the terpeneless oil is first fractionated and the process applied 
to both the first and the last fraction. Docker's method is not absolutely 
quantitative, as some terpenes will dissolve in the weak spirit, also because 
the transfer of the oils from the separatory funnel to the measuring burette 
always causes some loss. 

The main advantage of the terpeneless and^ especially of the sesquiter- 
ppnoless oils consists in their better solubility in dilute alcohol. The em- 
ployment of these oils, therefore, ejects a considerable saving of alcohol in 
the finished goods; odor and flavor of the oil are better utilized. A further 
advantage consists in the fact that, by the process of concentration, the oils 
are also freed of any products~bf decomposition or resinification which might 
result from improper handling or aging of the natural oils. Another merit 
of the terpeneless and sesqui terpeneless oils lies in their better stability. 
While natural citrus oils are apt to resinify, primarily due to polymeriza- 
tion of certain hydrocarbons, the concentrated oils are much more stable. 
Thus, they may be employed in powders, for the flavoring of gelatin desserts, 
for example, or for the scenting of bath salts. 

The introduction of terpeneless and sesquiterpeneless oils on the market 
has met with some resistance. Several authorities contend that the elimi- 
nation of terpcnes and sesquiterpenes removes also a part of the character- 
istic odor and flavor of the natural oil. The application of heat undoubtedly 
has some effect on the delicate flavoring constituents of the oil and, if im- 
properly prepared, concentrated oils may not display the freshness and 
bouquet of the original oil. Furthermore, the terpeneless and sesquiterpene- 
less oils contain a lower proportion of natural fixatives such as waxes and 
stearoptenes which contribute to the retaining of the flavor on the palate. 
Weighing the advantages against the disadvantages, the conclusion may be 
drawn that concentrated, terpeneless and sesquiterpeneless oils have their 
definite place in many formulas where highest possible concentration, solu- 
bility, and stability are required, but that they cannot replace the natural 
oils for all purposes. 



"Concentrated Citrus Oils," by A. H. Bennett, Perfumery Essential Oil Record 
25 (1934), 111. # 

"Preparation of Terpeneless Oils," by A. M. Burger, Riechstoff Ind. 13 (1938), 
217. Chem. Abstracts 33 (1939), 1089. 

"Removal of Terpenes from Essential Oils," by Pietro Leone, Riv. ital, essenze 
profumi 28 (1946), 5, 39, 82. Chem. Abstracts 40 (1946), 5201. 

"Terpeneless and Sesquiterpeneless Oils," by Y. R. Naves, Mfg. Chemist 18, 
No. 4 (1947), 173. 





Note. All temperatures in this book are given in degrees 
centigrade unless otherwise noted. 



"The Examination and Analysis of Essential Oils, Synthetics, and 
Isolates" describes the commercial methods of testing and evaluating the 
raw materials of the essential oil industry. Most of these methods have 
been used in the New York and Clifton laboratories of Fritzsche Brothers, 
Inc., during the course of many years. They frequently represent standard 
official procedures or modifications of such procedures. Many highly 
specialized techniques which are of value in the scientific examination of 
essential oils have not been included because they are seldom used in a 
commercial laboratory. 

Acknowledgment is due to the following standard reference works for 
much basic material used in the descriptions and discussions of these ana- 
lytical methods : 

"The United States Pharmacopoeias," United States Pharmacopoeia! 
Conventions, Washington, D. C. 

"The National Formularies," American Pharmaceutical Association, 
Washington, D. C. 

"The British Pharmacopoeias," General Council of Medical Education 
and Begistration of the United Kingdom, Constable & Co., London. 

"Official and Tentative Methods of Analyses of the Association of Agri- 
cultural Chemists," Association of Agricultural Chemists, Washing- 
ton, D. C. 

E. Gildemeister and F. Hoffmann, "Die iitherischen Ole," 3d Ed., 
Schimmel & Co., Miltitz, 1929-1931. 

S. Mulliken, "A Method for the Identification of Pure Organic Com- 
pounds," 1st Ed., John Wiley & Sons, Inc., New York, N. Y., 1904. 

Berichte, Schimmel & Co., Miltitz. 


The essential oil chemist works in a highly specialized field requiring 
careful analytical ability, ingenuity, and a highly developed sense of smell 
and taste. He must always be on the alert for known acjulterants and im- 
purities and for new and hitherto untried adulterants. Above all, he must 



have sufficient chemical background and experience to be able to interpret 
the results of his analyses. 

Crude adulteration of oils has lessened considerably, because of careful 
analytical control. Seldom does one encounter today the adulteration of 
lemon oil with turpentine, or the addition of acetanalide to vanillin. How- 
ever, some adulterations are still in evidence, especially where strict an- 
alytical control is not maintained by government agencies and buyers. 
For example, at a comparatively recent date, the orange oils of French 
Guinea were so badly adulterated with kerosene and mineral oil fractions 
that the reputation of this oil suffered; government control entirely chocked 
this gross adulteration. Ceylon citronella oils have been adulterated with 
mineral oil fractions for so long that the trade has almost accepted this as a 
necessary evil, trying to limit the amount of adulteration rather than to 
stop it altogether. Such crude adulterations usually offer no problem to the 
CvSsential oil chemist. A routine analysis easily discloses such falsifying. 

A much more dangerous and common type of adulteration is the addi- 
tion of materials that do not materially affect the physicochomical proper- 
ties of an oil. Often materials are added that arc normal constituents of 
the oil : materials that are obtained as by-products, isolates from other oils, 
or synthetics. Such "sophistication" is much more difficult to detect and 
often may be suspected but proved only with great difficulty at best. 

It is in cases such as these that a well-developed sense of smell and taste 
proves of immense value. Here it is important for the chemist to know 
what adulterants to expect. Organoleptic tests, in conjunction with 
physicochemical analyses, also are of great importance in evaluating the 
quality of unadulterated oils. 

A discussion of the general procedure to be followed in examining an 
essential oil, isolate, or synthetic may prove of value. 

A study of the odor, and in some cases the flavor, helps materially in 
detecting adulteration or "sophistication," and in judging quality. Com- 
parison should be made with an oil of high quality, a "type" oil of known 
purity. A drop or two of the oil in question is placed upon a strip of blotting 
paper ; the same amount of the pure "type" oil is placed upon a second strip ; 
and the two held together at right angles by means of a clip. 1 The odor of 
the two oils should be studied carefully and compared at intervals. When 
first on blotters, addition of the more volatile adulterants is often discovered. 
Solvent "by-notes" may also be detected in the case of a product obtained 
by extraction. When the blotters have dried considerably, addition of the 
less volatile adulterants may often be detected materials such as cedarwood 
and heavy camphor oil. The study of the odor and flavor often suggests 
the presence of adulterants which may be confirmed by special chemical or 

1 The wooden clips sold for drying photographic negatives prove very satisfactory. 


physical tests. Or adulterants indicated by the analysis may be confirmed 
by a study of the odor and flavor. Moreover, organoleptic tests are prob- 
ably the only satisfactory method, thus far developed, of detecting burnt, 
pyroligneous "by-notes" resulting from improper distillation, and of detect- 
ing slight spoilage in certain oils, as for example the citrus oils. 

Also of great importance is the determination of the physical and chem- 
ical properties of a given oil. The specific gravity, the optical rotation, the 
solubility in dilute alcohol, and the refractive index should be determined for 
all oils and liquid isolates and synthetics as a matter of routine. Other 
special tests are also to be carried out, depending upon the material 
under consideration (e.g., ester content, total alcohol determination, con- 
gealing point, evaporation residue). For an optically inactive, crystalline 
solid, the best criterion of purity lies in the determination of the melting 

Comparing these analytical figures with results of previous analyses and 
with data published in the literature, the chemist may obtain an indication 
of the purity and quality of the oil. Crude adulteration often is discov- 
ered at this point. 

The relationship between the individual chemical and physical proper- 
ties is often very revealing. Thus, the addition of orange terpenes to an 
orange oil will cause a lowering of the specific gravity, refractive index, and 
the evaporation residue, and a corresponding increase in the optical rota- 
tion ; the addition of turpentine oil will cause a lowering of the optical rota- 
tion as well as of the othor three properties. 

Another factor to be considered is possible sources of adulteration or 
contamination. Benzaldehyde should be tested for chlorine, since a posi- 
tive halogen test would indicate manufacture from benzyl chloride or in- 
sufficient purification. Low refractive index and specific gravity of a linaloe 
oil suggest adulteration with ethyl alcohol, a common form of adulteration 
for this oil. 

The value of the relationship between each physical and chemical prop- 
erty, and between the analysis and the odor and flavor cannot be stressed too 

The analytical figures obtained in as complex a material as an essential 
oil seldom represent actual percentages of single constituents. Thus, in the 
case of an ester determination, all saponifiable material is calculated as a 
certain ester, regardless of the fact that itnquestionably other esters are 
present or that other constituents are capable of saponification. The figures 
obtained, however, are no less valuable for practical purposes. Neverthe- 
less, it may be seen that in this field of chemistry it is of utmost importance 
that a procedure be rigidly followed in order to assure reproducible results 
that are of practical value. 


The main purpose of the following discussion is to help standardize such 
analytical procedures so that chemists throughout the essential oil industry 
may obtain results that can be reproduced by other workers in this field as 
well as by chemists in related industries. 


It is important that the sample used for analysis be representative of the 
entire contents of the container. Since most materials encountered by the 
analyst are homogeneous oils, sampling is not a difficult operation. How- 
ever, a few cautions are noted to assure a representative sample. 

Most essential oils are obtained by steam distillation with subsequent 
separation of the oil and water layers ; therefore, shipments of oil frequently 
contain water. If the oil has a specific gravity of less than 1.0, the water 
will be found at the bottom of the drum. It is a wise precaution to test each 
drum for water by introducing a sampling thief made of a long glass tube 
with one end slightly constricted. With the other end of the glass tube 
securely closed (by pressing the thumb over the opening), the thief is intro- 
duced into the drum and lowered until the constricted end just touches the 
bottom of the drum; the thumb is removed to permit the oil and water (if 
present) to enter the tube; the thumb is replaced and the tube withdrawn 
(the thief should be held in a vertical position). The oil within the tube is 
permitted to drain into a flint glass bottle or graduate. Any water, sedi- 
ment (e.g., dirt and rust) or precipitated waxes are readily discernible. 
For oils that have a specific gravity greater than 1.0, any water that is 
present will appear as a supernatant layer. Hence, in introducing the thief, 
the tube is not closed with the thumb and is lowered into the drum slowly. 

The sample in the flint bottle or graduate should receive a cursory ex- 
amination color, clarity, viscosity, the presence or absence of sediments, 
separated waxes, and water, all should be observed and noted; finally the 
odor of the sample should be studied. Oils stored in drums for long periods 
will frequently show a slight musty "by-note" which rapidly disappears; 
this is a typical "drum-note" and does not reflect adversely on the quality 
of the oil. Freshly distilled oils frequently show a slight, sharp empyreu- 
matic or burned note which disappears as the oil is aged. The "drum-note" 
and the "freshly distilled note" should disappear if the oil is permitted to 
stand in an open graduate overnight. If such notes do not disappear, the 
oils should be examined more carefully; it may be necessary to aerate the 
oil to remove persistent "by-notes." A small sample of the oil (about 50 cc.) 
should be treated by bubbling air through the oil for a period of several 
hours. It may be necessary to warm the air which is bubbled through the 
oik Diagram 4.1 shows a convenient apparatus for carrying out such 



teration. If this treatment yields a satisfactory oil, the contents of the 
Irum may be treated similarly. 

Citrus oils frequently deposit large amounts of waxes. These are easily 
observed by the water testing technique described above. Another indica- 
tion is the "feel" of the tube as it hits the bottom of the drum. 


To Water Pump 

DIAGRAM 4.1. Apparatus for the aeration of essential oils. 

If the drum shows no evidence of water or insignificant amounts of water 
and sediment, the sample drawn may be used for analysis. If water, wax, 
or sediment is present to a large extent, a fresh sample should be drawn from 
the supernatant oil. 

When the sample is received by the chemist, it should be clarified and 
freed from sediment and separated waxes by decantation or by filtration if 
necessary. A small amount of dry sodium chloride placed in the folded 
filter will frequently aid in removing traces of water and will remove the 
haze from an oil. Treatment with clay or kieselguhr may be necessary to 
remove a haze caused by suspended materials. If the oil is very dark in 
color owing to the presence of heavy metals or other metallic impurities, 
the color may be lightened by shaking with tartaric acid and filtering (see 
p. 311). The color and appearance of the oil both before and after treat- 
ment should be described in the analytical report, as well as the treatment 

Because of possible variation in the oils of a shipment of more than one 
drum, it is l>est to sample each drum of oil. However, if the oils are to be 
bulked (e.g., several drums are to be pumped into a tank to yield a uniform 
lot), an average or representative sample may be made based on the weights 
of the oil in the individual drums. The odor and general appearance of each 
drum should be examined before such a sample is made, to prevent the addi- 
tion of a drum of poor quality to the tank. If this average sample is found 
to be of inferior quality or shows any abnormalities, then each drum must 
be resampled and examined individually. 

Oils that congeal at temperatures normally encountered should be given 
special attention. These drums should be permitted to stand in a warm 


place and stirred occasionally (or heated in a steam room if the congealing 
point is high) until the last trace of solid material is dissolved. Anise oil 
may be taken as a typical example. During the cold weather a drum may 
be received in a frozen condition. Upon standing in a warm place, the 
anethole slowly melts until the drum is half solid, half liquid. The solid 
settles to the bottom. If a sample of the liquid portion is drawn, it will be 
deficient in anethole and may fail to meet the official requirements of "The 
United States Pharmacopoeia" ; such a sample would not be representative 
of the drum. Synthetics and isolates such as anethole, benzyl benzoate and 
diphenyl oxide usually require a steam room to melt them completely to 
assure a representative sample. Upon chilling or long standing, some oils 
deposit small amounts of crystalline materials such as menthol, cedrol, or 
camphor; in these cases, the oil should be gently warmed and stirred to re- 
dissolve the crystalline material before a sample is drawn. 

In sampling materials other than oils, certain precautions should be ob- 
served. For resinoids, oleoresins and balsams the drum or can should be 
stirred well with a flat stick to assure thorough mixing. A sample should 
not be drawn before the material is uniform. This is of importance for 
items such as styrax, which usually shows a separation of styrene, poly- 
styrene and water. 

The sampling of crude drugs offers considerable difficulties. "The 
United States Pharmacopoeia" 2 gives four methods for the sampling of 
vegetable drugs from original containers to obtain an "official," representa- 
tive sample. 

/. "It is recommended that gross samples of vegetable or 
animal drugs in which the component parts are 1 cm. or less in 
any dimension, and ail powdered or ground drugs, be taken by 
means of a sampler which removes a core from the top to the 
bottom of the container, not less than two cores being taken in 
opposite directions; that when the total weight of the drug to 
be sampled is less than 100 kilos (200 pounds) at least 250 g. 
shall constitute an official sample. When the total weight of the 
drug to be sampled is in excess of 100 kilos, repeated samples 
shall be taken by the above method, and according to the sched- 
ule given below, mixed and quartered, two of the diagonal quar- 
ters being rejected, the remaining two quarters being combined 
and carefully mixed, and again subjected to a quartering process 
in the same manner until two of the quarters weigh at least 
250 g., which latter quarters shall constitute an official sample. 

II. "It is recommended that gross samples of vegetable 
drugs in which the component parts are over 1 cm. in any dimen- 
sion be taken by hand. When the total weight of the drug to 
be sampled is less than 100 kilos, at least 500 g. shall constitute 

8 Thirteenth Revision, 710. 


an official sample, and this shall be taken from different parts of 
the container or containers. When the total weight of the 
drug to be sampled is in excess of 100 kilos, repeated samples 
shall be taken by the above method and according to the sched- 
ule below, mixed and quartered, two of the diagonal quarters be- 
ing rejected, and the remaining two quarters being combined 
and carefully mixed, and again subjected to a quartering process 
in the same manner until two of the quarters weigh not less than 
500 g., which latter quarters shall constitute an official sample. 

Schedule Recommended for Sampling 

Number of Packages Number of Packages 

in Shipment To He Sampled 

1 to 10 1 to 3 

10 to 25 3 to 4 

25 to 50 . 4 to 6 

50 to 75 6 to 8 

75 to 100 .... 8 to 10 

When over 100, the total number sampled should not be less than 10. 

III. "When the total weight of a drug to be sampled is 
less than 10 kilos it is recommended that the above methods be 
followed but that somewhat smaller quantities be withdrawn, 
and in no case should the final official sample weigh less than 
125 g. 

IV. "In addition to the withdrawing of official samples ac- 
cording to methods /, //, and ///, the official sample may consist 
of the total amount of a direct purchase made by Federal, State, 
or Municipal Food and Drug Act enforcement officials." 

The sampling of a pure chemical which is a solid (e.g., vanillin) will now 
be considered. The well-known method of quartering 3 will assure a repre- 
sentative sample. Most manufacturers give an identifying number to each 
batch manufactured, and consequently it may be assumed that each batch 
is uniform so that a sample taken at random will be representative of the 
whole batch. 

The final sample should be transferred to a bottle of light-resistant 4 

8 Treadwell and Hall, "Analytical Chemistry," John Wiley & Sons, Inc., New York, 
Vol. II (1942), 45. 

4 "The United States Pharmacopoeia" (Twelfth Revision, 6) defines a light-resistant 
container as "a container which is opaque, or designed to prevent photochemical deteriora- 
tion of the contents beyond the official limits of strength, quality, or purity, under customary 
conditions of handling, storage, shipment, or sale. 

"Unless otherwise directed, a light-resistant container shall be composed of a substance 
which in a thickness of 2 mm. shall not transmit more than 10 per cent of the incident radia- 
tion of any wave length between 2900 and 4500 angstrom units. 

"If the immediate container in its construction is less than 2 mm. in thickness, the same 
10 per cent limit of light transmission shall apply. 

"If the immediate container in its construction is not light-resistant, it must be provided 
with an opaque covering, be enclosed in an opaque covering or in an opaque container." 

(The definition of the Thirteenth Revision, 5, is essentially the same.) 


glass (amber, blue or green). The bottle should be well filled to prevent 
adverse action by the air and well stoppered with a sound cork. Screw caps 
should be used with caution, since the liners may contaminate the oil. 5 If 
a screw cap is to be employed it is well to stopper the bottle with a cork 
before using the screw cap. 

If the shipment of oil is to be stored for any appreciable length of time, 
the precautions noted below should be observed : 

1. The oils should be clarified and thoroughly dried. 

2. The oils are best stored in glass containers in a cool 6 place protected 
from light and air. Half filled containers should be avoided. Storage in 
glass is frequently impractical; if drums or cans must be used, heavily 
galvanized or heavily tinned iron usually will prove satisfactory. Alumi- 
num 7 and stainless steel can be used with some oils, but not universally. 

3. Certain oils are much more susceptible to oxidation and polymeriza- 
tion than others; oils rich in terpenes (e.g., citrus oils) and oils containing 
large amounts of aldehydes (e.g., benzaldehyde) are readily affected. Some 
oils (e.g., vetiver, sandalwood and patchouly) show very good keeping quali- 
ties and may actually improve upon aging. 

4. In general, the use of antioxidants for essential oils is not necessary 
if the oils are properly and carefully stored.* 


Specific gravity is an important criterion of the quality and purity of an 
essential oil. Of all the physicochemical properties, the specific gravity 
has been reported most frequently in the literature. Values for essential 
oils vary between the limits of 0.696 and 1.188 at 15 ; 9 in general, the 
gravity is less than 1.000. For each individual oil, however, the limits are 
much narrower and in most cases have been established during the course of 

5 The laboratories of Fritzsche Brothers, Inc., repeatedly have examined samples con- 
taminated by such liners the oils are frequently hazy, difficult to clarify, and show a 
strongly positive Halogen Test. 

6 Preferably at temperatures not exceeding 20. 

7 Many aluminum containers are lacquer lined ; often the oil will act as a partial solvent 
for the lacquer and introduce contaminating material. 

8 The importance of proper storage of oils is evidenced by the following observations : 
Italian lemon oils, stored under optimum conditions for four years, retained their fresh 
character; orange oils, stored experimentally under adverse conditions, spoiled within one 
week, developing the characteristic terbinthinato dor. The laboratories of Fritzsche 
Brothers, Inc., examined various oils that had beec roperly stored for more than fifty 
years : many of these oils showed no signs of spoilage v hatsoever, in spite of the fact that 
no chemical antioxidants had been used. 

Gildemeister and Hoffman, "Die atherischen Ole," 3d Ed., Vol. I, 699. 


The specific gravity of an essential oil at 15/15 may be defined as the 
ratio of the weight of a given volume of oil at 15 to the weight of an equal 
volume of water at 15. 10 

For determination of this physical property, accuracy to at least the third 
decimal place is necessary. Therefore, hydrometers are practi- 
cally worthless and should not be used. The Mohr-Westphal 
balance may be used but it has the disadvantage that relatively 
large amounts of oil are required for a determination. Other 
types of specific gravity balances have been developed which 
require less oil and which have proven satisfactory. Pycnome- 
ters offer the most convenient and rapid method for deter- 
mining specific gravities. A conical shaped pycnometer having 
a volume of about 10 cc. with a ground-in thermometer and a 
capillary side tube with a ground glass cap proves very satis- 
factory (see Diagram 4.2). 11 Sprengel or Ostwald tubes give 
even more accurate results ; if desired they may be used. How- 
ever, a determination cannot be made as rapidly or as con- 
veniently. Cleaning these tubes will prove considerably more 
difficult and time consuming. A small Sprengel tube or a 
Gay-Lussac specific gravity bottle having a capacity of about DIAGRAM 4.2. 
2 cc. will often prove of value when only small amounts of oil y 
are available. For routine analyses the conical pycnometer as described 
above is recommended. 

Procedure: Clean the pycnometer by filling it with a satu- 
rated solution of chromium trioxide in sulfuric acid and allow 
it to stand for at least 3 hr. Empty the pycnometer and rinse 
thoroughly with distilled water. Fill the pycnometer with 
recently boiled distilled water which has been cooled to a tem- 
perature of about 12 and place it in a water bath, previously 
cooled to 12. Permit the temperature to rise slowly to 15. 
Adjust the level of the water to the top of the capillary side arm, 
removing any excess with a blotter or cloth, and put the ground 
glass cap in place. Remove the pycnometer from the water 
bath, dry carefully with a clean cloth, permit it to stand for 30 
min. and weigh accurately. Empty the pycnometer, rinse 

10 The density of a liquid is the weight of a unit volume. Thus, density may be ex- 
pressed in pounds per cubic foot, or more frequently in grams per cubic centimeter. At 
3.98 (the temperature of maximum density for pure water, free from air) 1 cc. of water 
weighs 0.099073 g. ; furthermore, at this temperature 1 ml. of water weighs exactly 1 g. 
Since the coefficient of expansion of wqtcr i r s small, the density of a liquid expressed in grains 
per cubic centimeter corresponds doyly to the specific gravity. However, the fundamental 
difference in the two concepts shout* be thoroughly understood. 

11 This pycnometer is similar to that described in A.S.T.M. Designation D 153 with the 
exception that the capacity is approximately 10 cc. instead of 50 cc. 


several times with alcohol and finally with ether. Remove the 
ether fumes with the aid of an air blast and permit the pycnome- 
ter to dry thoroughly. Weigh accurately after standing 30 
min. The "water equivalent" of the pycnometer may be found 
by subtracting the weight of the empty pycnometer from its 
weight when full. 

Fill the clean, dried pycnometer with the oil previously 
cooled to a temperature of 12. Following the same procedure 
as above, place the pycnometer in a water bath and permit it 
to warm slowly to 15. Adjust the oil to the proper level, put 
the cap in place, and wipe the pycnometer dry. Accurately 
weigh after 30 min. 

The weight of the oil contained in the pycnometer divided 
by the water equivalent gives the specific gravity of the oil at 
15/15 (in air). 

For a given pycnometer the water equivalent need be 
determined only once; therefore, it is important that this de- 
termination be performed with great care and accuracy. 

For scientific work or for cases where the gravity is in question, the de- 
termination should be carried out exactly as described above. However, 
for routine analyses it is permissible to determine the specific gravity of an 
oil at room temperature compared with water at 15 and then to reduce 
this value to a temperature of 15/15 by use of a proper correction factor. 
Numerous workers have determined correction factors for various oils and 
have recommended a general value from 0.00042 12 to ().(XK)84 13 per degree 
centigrade. However, as Bosart 11 pointed out, it would be unsatisfactory 
to take the average figure obtained from a variety of oils and apply it to a 
particular oil, all the more so when there is a difference of opinion as to what 
that figure should be. 

In the investigation carried out by Bosart, values were obtained which 
ranged from 0.00070 to 0.00099 per degree 15 for the forty-two essential oils 
he examined. For synthetics and isolates normally encountered by the 
essential oil chemist or perfumer, values ranged from 0.00007 to 0.00114 per 
degree. 16 Hence, it is unjustifiable to use an average correction factor if 

12 Harvey, J. Soc. Chem. Ind. 24 (1905), 717. Ber. Schimmd A Co., October (1005), 87. 
18 Schreiner and Downer, Pharm. Arch. 4 (1001), 167. Those authors determined the 

15 20 25 
specific gravity of thirty-two essential oils at -~, , ; they recommended the use of the 

factor, 0.0064 per degree. Bosart has recalculated this figure in order to convert the specific 

25 15 

gravity at to , and lias arrived at the factor 0.00084. 
lo lo 

" Ind. Eng. Chem., Ind. Ed. 28 (1936), 867. 

16 Ibid. 

u Perfumery Essential Oil Record 30 (1939), 145. 



accurate data are to be obtained. A summary of Bosart's work is given in 
Table 4.1 and Table 4.2. 


Almond, Bitter. 


Linaloe ... 








Orange, Sweet 


Bois de Rose, Brazilian . . . 


Palmarosa . . 












Peppermint . . 




Petit grain 




Pine . 


Citronella, CYylon . . . 
Citronella, Java. . . . 


Sandalwood, East Indian . . 
Sassafras, Artificial 


Eucalyptus (Kucalitptiis globulus) 

Spearmint . 


70 to 80% 




Geranium, African . 




Geranium, Bourbon . . 






Wintergreen (Gaultheria 


Lemon grass. . 


Ylang Ylang . . 


The proper correction is to be added if the temperature, at which the 
determination was made, is above 15; conversely to be subtracted if the 
temperature is below 15. These correction factors may also prove of use 
for converting specific gravities given in the literature at temperatures other 
than 15 when compared with water at 15. 

It is customary to report specific gravities for essential oils at 15/15. 
For oils that are not liquid at this temperature the specific gravity is con- 
veniently reported at some higher temperature, compared Avith water at 
15. Thus, the gravity of rose oils is often reported 17 at 30/15. "The 
United States Pharmacopoeia" and "The National Formulary" specify a 
temperature of 25/25 for most essential oils. "The British Pharma- 
copoeia" specifies 15.5/15.5. In order to convert the specific gravities 
from 15/15 to 25/25, the conversion factors given in Table 4.3 may be 
used. 18 These corrections are to be subtracted from the values determined 
at 15/15. 19 

17 "The United States Pharmacopoeia," Thirteenth Revision, 456. 

18 Ber. Schimmel <fe Co. April (1906), 73. 

19 A more exact determination will result if the water equivalent of the pycnometer at 
25 and the weight of the oil contained in the pycnometer at 25 are determined by the 
method described under "Procedure." 






Ethyl Propionate 










Allyl Alcohol 


Geranyl Acetate . 


Allyl Formate 




n-Amyl Acetate . 




o-Amyl Cinnamic Aldehyde .... 


Heptaldehyde . . . 


n-Amyl Ether 


Heptyl Alcohol 


Amyl Salicylate 




Anisic Aldehyde 


lonone ... . 




Isoamyl Acetate . ... 


Benzyl Acetate 


Isoamyl Formate 


Benzyl Alcohol 




Benzyl Benzoate 




Benzyl Ether 




Bornyl Acetate 


Lauryl Alcohol 


Brombenzene . . .... 






Linalool . ... 


n-Butyl Acetate . 


Linalyl Acetate 


n-Butyl Benzoate 


Methyl Acetate 


n-Butyl n-Butyrate. 


Methyl Acetophenone 


n-Butyl Formate 
n-Butyl Lactate 


Methyl Anthranilate 
Methyl Benzoate. . 


n-Butyl Propionate . 


Methyl n-Butyrate 


n-Butyl d-Tartrate 


Methyl n-O&proate 




Methyl Formate 


n-Caproic Acid 


Methyl Heptenone 


n-Caprylic Acid 


Methyl Nonyl Ivotono 




Methyl Phenylacotate 




Methyl Phthalate 


Cinnamic Aldehyde 
Cinnamyl Alcohol . 


Methyl Propionate 
Methyl Salicylate 








Octyl Alcohol 






p-Crcsyl Acetate 


Phenyl Acetate 


p-Cymene . 


Phenylethyl Acetate . . 


Decyl Alcohol 


Phenylethyl Alcohol 


Diethyl Phthalate 


Phenylpropyl Alcohol 




Pinene .... 


Diphenyl Methane 


7i-Propyl Acetate 

0001 1C 

Diphenyl Oxide 


n-Propyl Formate 


Ethyl Acetate . 




Ethyl Benzoate 



00008 ( 

Ethyl n-Butyrate. 


Salicyl Aldehyde 


Ethyl Caproate (Tech ) 




Ethyl Formate 


Terpinyl Acetate 


Ethyl n-Heptoate 


Valeric Acid 




15 25 


15 25 





Almond Bitter 






Sandalwood . ... 

Cajuput . . . 

Cassia Rectified 





Sweet Birch (Belida lento) . . . 





Turpentine, Rectified 
Wintergreen (Gaultheria 

Erigeron . .... 

Eucalyptus (Kwnli/ptus globulua) . . 

Juniper Berries 

SN nthetic 

Cinnamic Aldehyde 





Methyl Salicylate 

Orange, Sweet 



Most essential oils when placed in a beam of polarized light possess the 
property of rotating the plane of polarization to the right (dextrorotatory), 
or to the left (hicvorotatory). The extent of the optical activity of an oil 
is determined by a polari meter and is measured in degrees of rotation. Of 
the numerous types of polarimeters that are available, the most convenient 
for use with essential oils is probably the half-shadow instrument of the 
Lippich type. 20 

The angle of rotation is dependent upon the nature of the liquid, the 
length of the column through which the light passes, the wave length of the 
light used, and the temperature. 

Both the degree of rotation and its direction are important as criteria of 
purity. In recording rotations it is customary to indicate the direction by 
the use of a plus sign (+) to indicate dextrorotation (rotation to the right, 

50 For a discussion of the theory involved, the reader is referred to H. Landolt: "The 
Optical Rotating Power of Organic Substances and Its Practical Application" (translated 
by J. H. Long), The Chemical Publishing Co., Boston, Pa. (1902). Landolt thoroughly 
covers the field of optical activity, including, inter alia, the causes of optical activity and 
inactivity, the theory and construction of the polarimeter, and the various types of instru- 
ments available. 


i.e., clockwise) or a minus sign ( ) to indicate laevorotation (rotation to the 
left, i.e., counterclockwise). 

Since the scale reading for an optically active liquid is directly propor- 
tional to the length of the transmitting column of liquid, it is necessary to 
use a standard tube, 100 mm. long. If for any reason a longer or shorter 
tube is used, the rotation should be calculated for a tube of 100 mm. and 
reported as such. Rotations for essential oils given in the literature may be 
assumed to be for this standard tube unless a different length is specified. 

It has become customary in polarimetric work to use sodium light. A 
suitable source may be obtained by placing large crystals of sodium chloride 
upon the grid of a Meeker burner or by wrapping a piece of asbestos, pre- 
viously saturated in a strong salt solution, around the conventional Bunsen 
burner. By far the most convenient and satisfactory method of maintaining 
a constant light source is the use of a sodium vapor lamp. Such lamps, 
designed especially for use with polarimeters, are available. 

Although "The United States Pharmacopoeia" and "The National 
Formulary" specify 25 as the official temperature for all optical rotations, 
nevertheless, a standard temperature of 20 is usually adopted for essential 
oils reported in the literature. For most essential oils the change in optical 
rotation with temperature variations normally encountered in the laboratory 
is very small; hence, in routine analyses the readings are usually taken at 
room temperature. No corrections for temperature variations are made 
except in the case of citrus oils which contain large amounts of highly active 
terpenes. The corrections to be used, per degree centigrade, are : 

Orange Oil 13.2' 

Lemon Oil 8.2' 

Grapefruit Oil 13.2' 

The proper correction is to be added if the reading is taken at a tempera- 
ture higher than the desired temperature and, conversely, to be subtracted 
if the temperature of the reading is lower than the desired tempera tu re. 

In scientific work the temperature at which the rotation was determined 
should be specified. To adjust the temperature to standard, the polari meter 
tubes may be immersed in a constant temperature bath. Use may also be 
made of special water jacketed tubes. 

All determinations should be carried out in a dark room. Monochro- 
matic sodium light should be employed. 

a. Liquids. The oil or liquid should be free from suspended material. 
Often oils are hazy owing to the presence of small amounts of water; such 
an oil should be dried with anhydrous sodium sulfate and filtered before a 
determination is attemoted. 


Procedure: Place the 100 mm. polarimeter tube containing 
the oil or liquid under examination in the trough of the instru- 
ment between the polarizer and analyzer. Slowly turn the 
analyzer until both halves of the field, viewed through the tele- 
scope, show equal intensities of illumination. At the proper 
setting, a small rotation to the right or to the left will imme- 
diately cause a pronounced inequality in the intensities of 
illumination of the two halves of the field. 

Determine the direction of rotation. If the analyzer was 
turned counterclockwise from the zero position to obtain the 
final reading, the rotation is laevo ( ); if clockwise, dextro 


After the direction of rotation has been established, care- 
fully readjust the analyzer until equal illumination of the two 
halves of the field is obtained. Adjust the eyepiece of the tele- 
scope to give a clear, sharp line between the two halves of the 
field. Determine the rotation by means of the protractor; 
read the degrees directly, and the minutes with the aid of either 
of the two fixed verniers; the movable magnifying glasses will 
aid in obtaining greater accuracy. A second reading should be 
taken; it should not differ by more than 5' from the previous 

Some oils are too dark in color for an accurate determination of the 
optical rotation when a 100 mm. tube is used. In such cases, a 50 mm. tube 
may be employed, or even a 25 mm. tube, if necessary. Since the rotation 
is reported for a MX) mm. tube, any experimental error will l>e multiplied by 
2 for a 50 mm. tube, and by 4 for a 25 mm. tube. Conversely, if a clear, 
light colored oil is examined which is only slightly optically active, the use 
of a longer tube (200 mm.) may often prove of advantage; the value to be 
reported will be found by dividing the observed rotation by 2; any experi- 
mental error will also be halved. 

6. Solids. The optical activity of a solid is best determined in solution 
and expressed as specific rotation. The following formulas may be used: 

r -, a /1N 

Mn' =-~ (1) 

MD- = 5 (2) 

21 Since most, instruments are calibrated only to 180, some confusion may exist as to 
the direction of rotation ; t his is especially true if the liquid is highly optically active. Thus, 
a reading of -f 100 may be reported mistakenly as a reading of 80. If any doubt exists 
in the mind of the chemist, the determination should be repeated using a 50 mm. tube. 
In the example given alxwe, a reading of -|-50 would l>e obtained, indicating that the cor- 
rect value for a 100 mm. tulx) is -f-100; the other possible reading with the smaller tube 
(that is, - 130) corresponds to a value of -260 for a 100 mm. tube: so high a value would 
be most unusual for an essential oil. The optical rotation of an essential oil seldom is 
greater than 100. 


where : [a]o <0 = specific rotation at temperature t, using sodium light ; 

a = observed rotation in degrees of the solution at tempera- 
ture t, using sodium light ; 

I = length of polarimeter tube in decimeters ; 

d = specific gravity of the solution at the temperature t ; 

p = concentration of the solution expressed as the number of 
grams of active substance in 100 g. of solution ; 

c = concentration of solution expressed as the number of grams 
of active substance in 100 cc. of solution. 

Formula (2) is more convenient, since it does not require the determination 
of the specific gravity of the solution. 

The experimental value for the specific rotation of a solid is dependent 
upon the concentration of the solution and upon the particular solvent em- 
ployed ; therefore, the concentration and solvent used should be given when 
the specific rotation of a solid is reported. The rotation should be de- 
termined as soon as possible after the solution has been prepared, so that 
any change that might result from mutarotation will be minimized. 

The use of specific rotation for a complex mixture such as an essential 
oil is not recommended. For the sake of completeness, the following formula 
is given: 

Wo" = 5 (3) 

Formula (3) applies to optically active liquids. 

The symbol []D' is reserved exclusively for specific rotation; optical 
rotation determined in a 100 mm. tube is indicated by an' , the brackets 
being omitted. If no temperature is given, it may be assumed that the 
optical rotation was determined at room temperature. 


When a ray of light passes from a less dense to a more dense medium, 
it is bent or "refracted" toward the normal. If e represents the angle of 
reffaction, and i the angle of incidence, according to the law of refraction, 

Smi = AT 
Sin c n 

where n is the index of refraction of the less dense, and N t the index of re- 
fraction of the more dense medium. 

Refractometers offer a rapid and convenient method for the determina- 
tion of this physical constant. Of the various types, the Pulfrich or the 


Abb6 refractometer proves very satisfactory. 22 The Abb6 type, with a range 
of 1.3 to 1.7, is recommended for the routine analyses of essential oils, the 
accuracy of this instrument being sufficient for all practical work. The 
readings may be made directly from the scale without consulting conversion 
tables; only one or two drops of the oil are required for a determination; 
the temperature at which the reading is taken may be adjusted conveniently. 

Procedure: Place the instrument in such a position that 
diffused daylight or some form of artificial light can readily be 
obtained for illumination. Circulate through the prisms a 
stream of water at 20. Carefully clean the prisms of the in- 
strument with alcohol and then with ether. To charge the 
instrument, open the double prism by means of the screw head 
and place a few drops of the sample on the prism, or, if preferred, 
open the prisms slightly by turning the screw head and pour a 
few drops of sample into the funnel-shaped aperture between 
the prisms. Close the prisms firmly by tightening the screw 
head. Allow the instrument to stand for a few minutes before 
the reading is made so that the sample and instrument will be 
at the same temperature. Move the alidade backward or for- 
ward until the field of vision is divided into a light and dark 
portion. The line dividing these portions is the "border line/' 
and, as a rule, will not be a sharp line but a band of color. The 
colors are eliminated by rotating the screw head of the com- 
pensator until a sharp, colorless line is obtained. Adjust the 
border line so that it falls on the point of intersection of the 
cross hairs. Head the refractive index of the substance directly 
on the scale of the sector. A second reading should be taken a 
few minutes later to assure that temperature equilibrium has 
been attained. 

Occasionally, the instrument should be checked by means of the quartz 
plate that accompanies it, using monobromnaphthalene, or if such a plate 
is not available, by means of distilled water at 20; the refractive index of 
pure water at this temperature is 1.3330. 

Great care should be exercised when determining refractive indexes 
during hot, humid weather, since moisture in the air may condense on the 
cooled prisms. This will result in a blurred and indistinct line of separation 
between the light and dark fields if the oil between the prisms does not dis- 
solve the condensed moisture ; if the oil dissolves the moisture, the dividing 
line will be sharp, but the observed index will be low. 

22 For a discussion of the theory involved and for a description of the instruments, the 
reader is referred to a standard text on physical chemistry, e.g., Findlay, "Introduction to 
Physical Chemistry," Longmans, Green <fe Co. (1033), 103; Daniels, Mathews, and 
Williams, "Experimental Physical Chemistry," McGraw-Hill Book Co., New York 
(1941), 44. 



It has become the accepted procedure to report refractive indexes for 
essential oils at 20, using a monochromatic sodium light source, 23 unless the 
material is a solid at that temperature. Thus, in the case of rose oil the 
refractive index is often given at 30 ; 24 in the case of anethole, at 25. 25 

Whenever possible, however, all observations should be made at 20. 
The use of factors to reduce readings to 20 is not recommended. Various 
investigators, notably Bosart, have reported the change of refractive index 
with temperature for numerous oils. According to the findings of Bosart, 26 
the values for the fifty-four oils examined lie between the limits of 0.00039 
and 0.00049 per degree centigrade, and for the forty-seven synthetics and 
isolates between the limits of 0.00038 and 0.00054. A summary of Bosart's 
work is given in Table 4.4 and Table 4.5. These tables may be used con- 


tion per 

tion IHT 

Almond Bitter 






Mace . 


Bay leaves. 








Bois de Rose 


Orange, Sweet 






Camphor, Brown, s.g, 0.95-0.97 . . 
Camphor s g 1 020 


Palmarohii ... . 


Camphor, white 


Peppermint. . . 




Petitgrain ... . ... 

0.0004 4 









Cinnamon, Ceylon 


Rosemary ... 

0.0004 4 

Citronella, Ceylon 


Sandal wood, I']. I. 


Citronella, Java 


Sassafras, Art. 
















Sweet Birch (Hetula lenta) 


Eucalyptus (Eucalyptus globulus) . 






Thyme Red 40-45% 


Geranium, African 



0.0004 (i 

Geranium, Bourbon 






Wintergreen (Gaultheria 







Ylang Ylang 




23 The Abbe* refractometer is calibrated for the D-line of sodium vapor light. 

24 "The United States Pharmacopoeia," Thirteenth Revision, 456. 
26 "The National Formulary," Eighth Edition, 51. 

28 Perfumery Essential Oil Record 28 (1937), 95. 




tion per 

tion per 



I lyd roxyci t ronellal 


tt-Ainyl Cinnaniic Aldehyde 




Amyl Salic vlate . . . 

000 12 

Isoeugenol. . . 


Anisic Aldehyde (Aubopine) 




Henzvl Acetate 




Bornyl Acetate . . . . 
Carvaerol, Tech. 
Oinnamic \lcohol 


Linalyl Acetate ... 
Methyl Anthranilatc. . . 
Methyl Benzoato 
Methyl Ileptcnono 


Oinnamic Aldehyde 


Methyl Phenylacetate 
Methvl Salicylato 


Citronrllal. ... 
C-it roiu'llol 


Nitrobenzene (Mirbane Oil) 


7>-C^re^vl Vcetati' 


Orange Terpenes 


T>-( /ymene 


Phony let hyl Acetate 


Diethyl Phthalate 
Diphenyl Oxide . . .... 


Phenylcthyl Alcohol. .. 
Phenyl Methyl Carhinyl Acetate 
Phenvlpropyl Alcohol 







0004 1 



Geranyl Acetate . 
(teranyl Butyrato 
(Jeranyl Formate. . 


Terpineol . 
Terpinyl Acetate 


voniontly to convert values reported in the literature at other than 20. 
If an oil is encountered which is not listed in the table, the use of a correction 
factor of 0.00045 per degree will give approximately correct results. If the 
refractive index is reported at a temperature above 20, the proper correc- 
tion must be added; conversely, if reported at below 20, the correction 
must be subtracted. 


It is beyond the scope of this work to treat thoroughly of molecular 
refraction. 27 However, a brief discussion of the fundamental concepts 
involved may prove useful. 

The index of refraction of a liquid varies with the temperature and with 
the wave length of the light. In order to obtain a constant which is inde- 
pendent of the temperature, Gladstone and Dale 28 introduced the use of 
"specific refractivity." Subsequently, Lorentz, 29 and Lorenz 30 independ- 

" Reference may he made to the original papers of Eisenlohr, of Swientoslawski, and of 
Brtthl and to any standard text on physical chemistry for further discussion of this interest- 
ing physical property. 

M Roy. Sor. London, Phil Trans. 148, Part I (1858), 887, 

Mnn. Physik Chem. N.S. 9 (1880), 641, 
11 (1880), 70, * 



ently deduced an expression for specific refractivity, based upon the electro- 
magnetic theory of light, which shows considerably less variation than the 
empirical expression of Gladstone and Dale. In order to compare the 
refractivities of different liquids, the use of molecular refractivity (molecular 
refraction) is necessary. This constant is equal to the product of the 
molecular weight of a substance and its specific refractivity. 
Using the Lorentz and Lorenz expression : 

R = Mr = 

where : R the molecular refractivity ; 
M = the molecular weight ; 
r = the specific refractivity ; 
n = observed refractive index at temperature t ; 
d = density at temperature t. 

The molecular refractivity has been found to be essentially additive. 
Hence, it is possible to calculate atomic refractivities for the different ele- 
ments from a series of molecular refractivities of different compounds. By 
means of these atomic constants, the molecular refractivity of a pure chem- 
ical compound can be calculated as the sum of the atomic refractivities. 


Eisenlohr (1910) 


Rrahl-Conrody (1.S91) 

CH 2 





2 501 

H ... 

1 100 

1 051 

1 051 




2 287 



1 679 

1 683 

O' . .... 

1 525 

1 517 

1 521 



5 976 

5 998 







14 120 

14 120 

Double bond between C-atoms . 
Triple bond between C-atoms . . 




* From Eisenlohr, "Spektrochemie organischer Vorbindungcn," Stuttgart, (1912), 44, 
46, 48. 

Investigation has shown, however, that the molecular refractivity is in- 
fluenced by the presence of double and triple bonds, and also by the consti- 
tution of the molecule. Table 4.6 gives values for atomic refractivities for 
the D line of the solar spectrum (sodium light), 5893 angstrom units, calcu- 
lated by different investigators. By use of these constants it is often pos- 
sible to establish or confirm the chemical constitution of a pure chemical 


Certain anomalies have been observed. When double bonds are present 
in a conjugated position, the molecular refractivity will show in general a 
higher value than one would expect; this is known as optical exaltation. 
In some cases optical depression is also encountered. It is interesting to 
note that conjugated double bonds in a ring compound cause no exaltation 
or depression. 

The application of molecular refraction is limited to pure individual 
chemical compounds; it becomes meaningless when applied to mixtures as 
complex as essential oils. Nevertheless, this constant has played a very 
important role in the elucidation of structure in the case of many individual 
constituents of essential oils after separation and purification. 


a. Solubility in Alcohol. Since most essential oils are only slightly 
soluble in water and are miscible with absolute alcohol, it is possible to de- 
termine the number of volumes of dilute alcohol required for the complete 
solubility of one volume of oil. The determination of such a solubility is a 
convenient and rapid aid in the evaluation of quality of an oil. In general, 
oils rich in oxygenated constituents 31 are more readily soluble in dilute 
alcohol than oils rich in terpenes. 

Adulteration with relatively insoluble material will often greatly affect 
the solubility. Sometimes an actual separation of the adulterant may be 
observed. For example, adulteration of citronella oils (which are normally 
soluble in 80 per cent alcohol) with relatively large amounts of petroleum 
fractions will result in a poor solubility for the oil in 80 per cent alcohol and 
an actual separation of oily droplets of the adulterant. However, certain 
oils will show a normal separation in dilute alcohol. Expressed orange oil, 
for example, will separate natural waxes in 90 per cent alcohol. In alcohol 
of lower strength such an oil will separate a terpene fraction in addition to 
the waxes. Use of this fact sometimes is made in the preparation of terpene- 
less and sesquiterpeneless oils, concentrates and extracts. 

The solubility of an oil may change with age. Polymerization is usually 
accompanied with a decrease in solubility; i.e., a stronger alcohol may be 
required to yield a clear solution. Such polymerization may be very rapid 
if the oil contains large amounts of easily resinified terpenes e.g., jumper 
berry oil, bay oil. Improper storage may hasten polymerization; factors 
such as light, air, heat, and the presence of water, usually exert an 

31 However, the oxygenated constituents belonging to the sesquiterpene series are rela- 
tively insoluble; e.g., cedrol, santalol. Several other exceptions are also encountered; e.g., 
safrole, anethole. 



unfavorable influence. Occasionally the solubility of an oil improves upon 
aging e.g., oil of anise. 32 

Alcohols of the following strengths are customarily used in determining 
solubilities of essential oils : 

50%-60%-70%-80%-90%-95% and occasionally 65% and 75%. 

These are volume percentages at 15.56/15.56. In preparing dilute alco- 
hols it is convenient to weigh the alcohol (95 per cent by volume) and the 
distilled water to give the proper volume percentage. Preparation in this 
manner is independent of temperature. The strength of the alcohol should 
be checked by determining the specific gravity at 15.56/15.56. Final 
adjustments may be made if necessary. 


(% by volume) 

Specific Gravity 

95% Alcohol 
by volume, (j? ) 

Water (g.) 
































Procedure: Introduce exactly 1 cc. of the oil into a 10 cc. 
glass-stoppered cylinder (calibrated to 0.1 cc.), and add slowly, 
in small portions, alcohol of proper strength. Shake the cyl- 
inder thoroughly after each addition. When a clear solution 
is first obtained, record the strength and the number of volumes 
of alcohol required. Continue the additions of alcohol until 
10 cc. has been added. If opalescence or cloudiness occurs 
during these subsequent additions of alcohol, record the point at 
which this phenomenon occurs. In the event that a clear solu- 
tion is not obtained at any point during the addition of the al- 
cohol, repeat the determination, using an alcohol of higher 

Since the solubility is dependent upon the temperature, all determina- 
tions should be made at 20. It should be noted, however, that "The Unitec 
States Pharmacopoeia" 33 and "The National Formulary" 34 specify an officia 
temperature of 25 for solubilities; "The British Pharmacopoeia," 36 a tern- 

82 This is due to the presence of the difficultly soluble anethole, which yields upon oxida 
tion the readily soluble anisic aldehyde. 

Thirteenth Revision, 8. 
' M Eighth Edition, 10. 
M (1932), 9. 


peraturc of 15.5. The proper temperature may be maintained by frequent 
immersion of the cylinder in a water bath previously adjusted to the desired 

If an oil is not clearly soluble in the dilute alcohols, it is advisable to 
describe more fully the appearance of the solubility test. 

The following terms, which are relative and entirely empirical, are used 
in the laboratories of Fritzsche Brothers, Inc., to describe the appearance 
of the solution : 

Clearly soluble Opalescent 

Slightly hazy Slightly turbid 

Hazy Turbid 

Slightly opalescent Cloudy 

A further term occasionally used is "fluorescent." 

In the case of turbidity or cloudiness, record any separation of wax or 
oil that occurs, as well as the period of time required for such separation. 

If an oil is soluble in a number of volumes of alcohol which is not a 
multiple of J, report the solubility as being between the closest such limits. 
For example, if 2.7 volumes of 70 per cent alcohol were required to obtain 
a clear solution, and the solution remained clear upon further additions of 
70 per cent alcohol until a total of 10 volumes had been added, the solubility 
would be recorded as : 

"Clearly soluble in 2.5 to 3 volumes of 70 per cent alcohol and more, up 
to 10 volumes." 

The behavior of the oil is best described by the following typical nota- 
tions : 

1. Clearly soluble in volumes of per cent alcohol and more, up 

to 10 volumes. 

2. Clearly soluble in volumes of per cent alcohol ; opalescent 

with more, up to 10 volumes. 

3. Clearly soluble in volumes of per cent alcohol; opalescent 

to turbid with more, up to 10 volumes. No separation observed after 24 hr. 

4. Clearly soluble in volumes of per cent alcohol and more, up 

to volumes ; opalescent in volumes and more, up to 10 volumes. 

5. Hazy in volumes of per cent alcohol ; cloudy with more, up 

to 10 volumes. Oily separation observed after hr. 

6. Clearly soluble up to 10 volumes of per cent alcohol. 

b. Solubility in Nonalcoholic Media. Several solubility tests have been 
introduced for the rapid evaluation of oils. The following have proven 


I. Carbon Disulfide Solubility for the Presence of Water** Oils rich in 
oxygenated constituents frequently contain dissolved water. This is par- 
ticularly true in the case of oils containing large amounts of phenolic bodies 
e.g., oil of bay. Such oils fail to give a clear solution when diluted with an 
equal volume of carbon disulfide or chloroform. This is the basis of a rapid 
test to ascertain whether or not an oil has been sufficiently dried. 

II. Potassium Hydroxide Solubility for Phenol-Containing Oils. Phenolic 
isolates and synthetics as well as oils consisting almost exclusively of phenolic 
bodies may be evaluated rapidly by dissolving 2 cc. of the oil in 20 or 25 cc. 
of a 1 N aqueous solution of potassium hydroxide 37 in a 25 cc. glass-stoppered, 
graduated cylinder. This test is particularly of value in the case of sweet 
birch and wintergreen oils. (See "Detection of Adulterants," p. 331.) 
It is well to examine critically the odor of the solution or any insoluble 
portion, whereby additions of foreign, odor-bearing substances may be 

Upon prolonged standing, the alkaline solution may saponify an ester 
group, if present. If the products of such a saponification are soluble in 
the alkaline solution, no separation will be observed e.g., methyl salicylate. 
If the products are not completely soluble, a separation may occur e.g., 
amyl salicylate. 

Solutions of the alkali phenolates are frequently good solvents for other 
compounds; thus terpeneless bay oils containing about 90 per cent eugonol 
often form clear solutions with a 1 N potassium hydroxide solution. In this 
connection see the discussion under "Phenol Determination," p. 293. 

///. Sodium Bisulfite Solubility for Aldehyde-Containing Oils. Oils 
(such as oil of bitter almond, free from prussic acid), and synthetics (such as 
benzaldehyde, tolyl aldehyde, cinnamic aldehyde, and anisic aldehyde) and 
isolates (such as citral) may reveal impurities by their incomplete solution 
in dilute bisulfite solution. This test is usually carried out in a 25 cc. glavss- 
stoppered, graduated cylinder: shake 1 cc. of the oil with 9 cc. of a freshly 
prepared saturated solution of sodium bisulfite and then add 10 cc. of water 
with further shaking. The odor of the resulting solution should be care- 
fully examined. Because of the relative insolubility of certain bisulfite addi- 
tion compounds, no general procedure is satisfactory for all aldehydes. 
Thus, some must be heated in a beaker of boiling water ; and some require 
a larger amount of water to yield a clear solution. Each chemist soon 

"The National Formulary," Sixth Edition, 272. 

37 The potassium Hydroxide Test Solution of "The United States Pharmacopoeia" 
(13th Rev., 842) may be used; this is prepared by dissolving 6.5 g. of potassium hydroxide, 
A.R., in sufficient water to yield 100 cc. of solution. Since the potassium phenolates are 
more soluble than the corresponding sodium compounds, the use of potassium hydroxide 
is to be recommended. 


develops his own techniques in testing these aldehydes; hence, specialized 
procedures have been omitted here. 


The congealing point 38 offers a distinct advantage over the melting point 
and the titer, in the case of mixtures, such as essential oils. 39 In determining 
the congealing point, the oil is supercooled so that, upon congelation, im- 
mediate crystallization with liberation of heat occurs. This results in a 
rapid rise of temperature, which soon approaches a constant value and 
remains at this temperature for a period of time. This point is known as the 
"congealing point. " With increasing percentage of crystalline material in 
an oil, the congealing point will approach a maximum. 40 Hence, this 
physical property is a good criterion of the percentage of such material. 
The congealing point is important in the evaluation of anise, sassafras and 
fennel oils. 

Procedure: Place about 10 cc. of the oil in a dry test tube of 
18 to 20 nun. diameter. Cool in water or in a suitable freezing 
mixture, the temperature of which should be about 5 lower than 
the supposed congealing point of the liquid. To initiate con- 
gelation, rub the inner walls of the tube with a thermometer, or 
add a small amount of the substance previously solidified by 
excessive freezing. The thermometer should be rubbed quickly 
up and down in the mixture in order to cause a rapid congela- 
tion throughout, witli its subsequent liberation of heat. The 
temperature should be read frequently; at first the rise of tem- 
perature is rapid, but soon approaches a constant value for a 
brief interval of time. This value is taken as the congealing 
point of the oil. 

The process described above should be repeated several 
times to assure obtaining the true congealing point. 

The thermometer used should be calibrated in 0.1 units and should be 
accurately standardized. A thermometer covering the range of 5 to 
+50 is satisfactory for most determinations. 

Before the oil is tested, it should be thoroughly dried with sodium sulfate, 
since the presence of small amounts of water will often materially lower the 
congealing point. 

In the case of sassafras oils, it is well to initiate the congelation by the 
addition of a small piece of solid safrole since sassafras oil can be congealed 
only with great difficulty if no "seed" is used. 

88 The so-called "congealing point" of rose oil is not a true congealing point, but is de- 
termined by the same method as that used for titer determinations in fixed oils. (See 
"Special Tests and Procedures/' p. 329.) 

39 The melting point is usually used for crystalline solids. 

40 This maximum will be the "congealing point" of the pure crystalline compound. 


For a more exact determination of the congealing point, the test tube 
containing the supercooled oil may be insulated by means of an air jacket. 
This is frequently of particular importance when determining congealing 
points which are much below room temperature, as, for example, the con- 
gealing point of euclayptus oils. Gildemeister and Hoffmann recommend 
the use of the Beckman apparatus, 41 frequently used for the determination 
of molecular weights by the lowering of the freezing point. The use of a 
larger sample (up to 100 cc.) may make the congealing point sharper. 


The importance of the determination of the melting point of a solid, 
crystalline material is obvious. 

A brief but comprehensive discussion of the determination of melting 
points has been given by Shriner and Fuson, 42 from which much of the fol- 
lowing is taken. 

Procedure: Heat a piece of 15 mm. glass tubing 43 in a flame 
until the glass is soft ; then draw out into a thin walled capillary 
tube about 1 mm. in diameter. Cut into lengths of about 6 cm., 
and seal one end in a name. Powder a small amount of the 
compound in a polished agate mortar and introduce some of 
the powder into the capillary tube. Hold the capillary tube 
vertically and gently rub with a file, which causes the powder 
to settle to the bottom ; pack the material by tapping the tube 
on the desk. Fasten the tube to the thermometer by means of 
a rubber band (cut from a piece of rubber tubing) so that the 
sample is close to the mercury bulb (see Diagram 4.3). Place 
a heavy white mineral oil in the beaker and heat with a low 
flame. Clamp a cylindrical metal shield, open at the top and 
bottom, in the position as shown in Diagram 4.3 in order to 
protect the flame from drafts. Heat at a rate to cause a rise 
in temperature of about 1 or 2 per min. Stir the oil bath 
continuously. Note the temperature at which the compound 
starts to melt 44 and that at which it is entirely liquid; record 
these values as the melting point range. Note also the tem- 
perature recorded by the auxiliary thermometer (t z ) ', the bulb 
of this thermometer should be placed midway between the sur- 
face of the oil and the top of the mercury thread in ti. Calcu- 
late the stem correction by means of the following formula : 

Correction = 0.0001 54 N (h - * 2 ) 

tt "Die atherischen Ole," 3d Ed. Vol. I, 707. 

41 "The Systematic Identification of Organic Compounds," John Wiley & Sons, Inc., 
New York (1940), 85. 

49 Soft glass test tubes are very satisfactory since the walls are relatively thin. 

44 According to "The United States Pharmacopoeia," Thirteenth Rev., 668, the tem- 
perature at which the column of the sample is observed to collapse definitely against the 
side of the tube at any point is defined as the beginning of the melting. The temperature 
at which the material becomes liquid throughout is defined as the end of the melting. 



where: N = number of degrees of mercury thread above the 

level of the oil bath ; 
(i observed melting point; 
<2 = average temperature of the mercury thread. 

This correction is to be added to the observed melting point. 

It is often time saving to run a preliminary melting point, raising the 
temperature of the bath very rapidly. After the approximate melting point 
is known, a second determination is carried out raising the temperature 
rapidly until within 10 of the approximate value and then proceeding slowly 
as described above. A fresh sample of the 
compound should be used for each deter- 

The thermometer should be calibrated by 
observing the melting points of several pure 
compounds such as the following : 

^ felt ing Point (rorr.) 



53 . 






Honzoic Acid 




Salicylic Acid 


Hippuric Acid 
I sat in 

216 . 


238 . 

. Carhanilido 




A r ,A r -Diacetylbenzidine 

Tr ,, . , ., , DIVC,R\M 4.3. Apparatus for the 

If the same apparatus and thermometer detorminatio n of melting point, 
are used in all molting point determinations, 

it is convenient to prepare a calibration curve. The observed malting 
point of the standard compound is plotted against the corrected value, and 
a curve is drawn through these points. In subsequent determinations the 
observed value is projected horizontally to the curve and then vertically 
down to give the corrected value. Such a calibration curve includes cor- 
rections for inaccuracies in the thermometer and stem correction. 

The use of short stemmed, standardized Anschiitz thermometers elimi- 
nates the need for an auxiliary thermometer and subsequent correction for 
emergent stem. 


It is important to record the melting point range of a compound since 
this is a valuable index of purity. A large majority of pure organic com- 
pounds melt within a range of 0.5 or melt with decomposition over a narrow 
range of temperature (about 1). 

When determining the melting point of a solid that readily sublimes 
e.g., borneol certain precautions become necessary. The rate of heating 
of the oil bath should be increased considerably. The capillary should not 
be introduced into the hot oil until the temperature is within 10 to 20 of 
the expected melting point. The use of a sealed capillary may be necessary, 
i.e., a capillary that has both ends fused. The use of a Fisher-Johns or 
similar type apparatus is not recommended for materials that sublime 

Other types of melting point apparatus have proven satisfactory e.g., 
the Fisher-Johns, Thiele, and Thiele-Dennis. 

If a compound has a high melting point a Maquenne block may con- 
veniently be used. It is claimed that the Dennis melting point apparatus 
is very satisfactory for compounds melting up to 300. 

Special types have been developed for determination of the melting 
point of waxes, 45 and the softening point of amorphous material. 46 


In the case of isolates and synthetics, the determination of the boiling 
range is an important criterion of purity. 

Procedure: Use the apparatus shown in Diagram 4.4. The 
bulb of the distilling flask should have a capacity of 50 cc. The 
neck of the flask above the side arm should be as short as pos- 
sible. The bottom of the flask rests in a circular opening, 2.5 
cm. in diameter, cut in a square piece of asbestos board having 
a thickness of about 3 mm.; this perforation should be slightly 
beveled on the upper edge to make it fit closely to the surface of 
the flask. 47 A wrapping of asbestos paper reaching to a point 
about 1 cm. above the side arm should be used to prevent con- 
densation due to drafts. 

Introduce 25 cc. of the sample into the flask by means of a 
pipette. Add a small clay chip. Insert the thermometer along 
the central axis of the flask with its bulb slightly below the side 
tube; attach a light auxiliary thermometer to the main ther- 
mometer to correct for stem exposure, the bulb of this second 
thermometer being placed half way from the cork to the top of 
the mercury column at the expected reading. (A short- 
stemmed thermometer of the Anschiitz type having the proper 

48 A.S.T.M. Melting Point Apparatus, Designation D87. 

46 A.S.T.M. Softening Point Apparatus (Ring and Ball Method), Designation D36. 

47 This is to prevent upward leakage of hot gases from the flame and subsequent super- 



range may be used ; this will require no correction for stem ex- 
posure.) Distill at a uniform rate of about 0.5 cc. per min. 
until the level of the liquid remaining in the flask falls to the 
level of the asbestos diaphragm. 

DIAGRAM 4.4. Apparatus for the determination of boiling range. 

Since some time will elapse before the thermometer can acquire the 
temperature of the vapor, little significance can be attached to readings 
taken before the end of the first minute after the fall of the first drop of 
distillate from the side tube. Any readings taken after the liquid falls 
below the level of the asbestos board will be greatly influenced by super- 
heating. In the case of pure compounds that boil without decomposition, 
the difference between the first and last significant readings should not 
amount to more than 1. 

The stem exposure correction may be found by the following formula: 

Correction = 0.000154 N(t v - f 2 ) 
where : N = number of degrees of emergent stem ; 

t\ observed temperature of main thermometer; 
ti = temperature of auxiliary thermometer. 

This correction is to be added. 

To reduce boiling points taken under pressures between 720 mm. and 
780 mm. to their approximate values at 760 mm., apply a correction of 0.1 
for every 2.7 mm. difference ; the correction is to be added if the observed 
pressure is below 760 mm. and to be subtracted if above 760 mm. 



The percentage of an essential oil which distills below a given temperature 
is frequently of importance in evaluating the oil ; also, the percentage which 
distills between certain limits. However, it must be remembered that when 
fractionating an oil, the quantitative results of different observers will 
vary greatly; this is due to differences in the types of distilling flasks and 
condensers employed, to the distillation rates, and to the degree of super- 
heating of the vapors. 

Examination of the various fractions is of great importance; the de- 
termination of physical and chemical properties of these fractions and a 
study of the odor is frequently very revealing. Furthermore, suspected 
adulterants may be tested for chemically, and if present identified by de- 

DIAGRAM 4.5. Apparatus for the determination of boiling ran go. 

Only through experience will the chemist know whether or not it is 
better to distill at atmospheric pressure or under vacuum. In general, for 
the collection of first fractions it is better to distill at atmospheric pressure. 
Usually it is more advantageous to separate fractions according to the tem- 
perature, measuring the volumes collected; occasionally it is desirable to 
collect definite amounts, noting the temperatures at which these fractions 
are obtained. 

For fractionations at normal pressure the following technique will gen- 
erally give satisfactory results. The procedure as described is intended 
primarily for the distillation of turpentine oil and for the removal and col- 
lection of the first. 10 npr ppnt. of pitnis ni!. 


Procedure: See Diagram 4.5. Place 50 cc. of the oil in a 100 
cc. three-bull) Ladenburg flask of approximately the following 
dimensions : the lower or main bulb 6 cm. in diameter, with the 
smaller condensing bulbs 3.5 cm., 3.0 cm., and 2.5 cm., respec- 
tively, in diameter; the distance from the bottom of the flask 
to the side arm, 20 cm. Support the flask in a hemispherical 
metal oil bath, 4 in. in diameter, containing a suitable heating 
medium such as glycerin, cottonseed oil, or high boiling mineral 
oil. Attach a Pyrex straight-tube condenser, 22 in. long, hav- 
ing a water cooled jacket, 48 and fitted with an adapter which is 
long enough to extend into the graduated cylinder used as a re- 
ceiver. Use a short-stemmed thermometer of the Anschutz 
type or a long-stemmed thermometer with an auxiliary ther- 
mometer for stem correction. Add a few small clay chips. 
Heat the bath with a Bunsen burner protected from drafts by a 
chimney. Fasten a large sheet of asbestos board vertically to 
act as a shield for the flame, bath and flask. Distill the oil at a 
uniform rate of 1 drop per sec. until the required distillate is 


An important criterion of purity is the evaporation residue; i.e., the 
percentage of the oil which is not volatile at 100. 

A determination of the evaporation residue is of special value in the case 
of the citrus oils; a low value for an expressed oil suggests the possibility 
of the addition of terpenes, or other volatile constituents; a high value may 
indicate the addition of foreign material, such as, rosin, fixed oils, or high 
boiling sesquiterpenes. In the case of rectified oils such as turpentine, a 
high value may indicate improper or lack of rectification, or polymerization 
due to age or improper storage. In the case of certain solids, such as cam- 
phor, thymol, or menthol, a high evaporation residue will indicate insufficient 

It is important to study the odor of an oil as it volatilizes during the 
heating. Often "by-notes" of foreign low boiling adulterants or contami- 
nants may be discovered. The odor of the final residue while still hot 
should also be carefully studied for the addition of high boiling adulterants, 
such as cedarwood. 

The consistency of the residue, both when hot and cool, and the color 
sometimes indicates the presence of particular adulterants. For example, 
an orange oil, which has a brittle residue instead of the usual soft waxy 
residue, should be carefully investigated for rosin. 

Acid numbers and saponification numbers may be determined on sus- 
picious residues: rosin usually raises the acid number considerably; fixed 
oils raise the saponification number. 

48 For oils containing mostly high boiling constituents (such as cassia and bay), use an 
air-cooled condenser. 


The fact that essential oils are complex mixtures makes an exact determi- 
nation of the nonvolatile residue very difficult. "Constant weight" cannot 
conveniently be attained because of the fact that waxes and other high boil- 
ing nonvolatile material tend to retain or "fix" some of the lower boiling 
constituents. "The United States Pharmacopoeia" defines constant weight 
as the value obtained when "two consecutive weighings do not differ by 
more than 0.1 per cent, the second weighing following an additional hour, of 
drying." 49 Even after "constant weight," according to this definition, has 
been attained, further prolonged heating will give much lower results. 
Hence, a certain standardization of technique becomes necessary. 

Procedure: Weigh accurately (to the closest milligram) a 
well cleaned Pyrex evaporating dish that has been permitted 
to stand in a desiccator for 30 min. To this tared dish add the 
requisite amount of oil or solid (weighed to the closest centi- 
gram) and heat on a steam bath for the prescribed length of 
time. Then permit the evaporating dish to cool to room tem- 
perature in the desiccator and weigh (to the closest milligram). 
Calculate the nonvolatile residue obtained, the so-called 
"evaporation residue," and express as a percentage of the 
original oil. 

Size of Sample Period of Heating 

(0.) (hr.) 

Oil Bergamot 5 5 

Oil Grapefruit 5 6 

Oil Lemon 5 4* 

Oil Limes, Expressed 5 6 

Oil Mace 3 8 

Oil Mandarin 5 5 

Oil Nutmeg 3 8 

Oil Orange 5 4 

Oil Tangerine . ... 5 5 

Oil Turpentine .5 4J 

Oleoresin Capsicum 1 . 

Oleoresin Ginger J ' 

Camphor ... 2 4 

Copaiba 0.5 6 

Menthol 2 2 

Styrax 2 2 

Thymol 2 4 

Floral Waters 100 After last of liquid 

has evaporated, heat 
for an additional 

It is well to bear in mind that the size, shape, aiid composition of the 
evaporating dish employed in such a determination, as well as the size of 
sample and time of heating, will influence the analytical result obtained. 

49 Twelfth Revision, 3. The Thirteenth Revision, 7, limits the difference to not more 
than 0.05%. 


Flat bottom evaporating dishes of Pyrex glass are very satisfactory; they 
offer the further advantage of more easily permitting an observation of the 
color and opacity of the residue. Conventional Pyrex evaporation dishes, 
80 mm. in diameter and 45 mm. deep, are to be recommended. The use of 
such dishes tends to minimize the formation of polymerization products in 
most cases. 

Certain exceptional products will require special treatments, however; 
evaporation residues on such materials as diacetyl are meaningless because 
of the rapid formation of polymerization products unless the determinations 
are carried out in vacuum with the application of little or no heat. 

In evaluating oleoresins, evaporation residues should also be determined. 
Here it is best to express the results as "loss of weight on heating/' The 
analytical results obtained will include the loss of volatile solvent as well as 
the loss of part of the naturally occurring essential oil. An abnormally high 
value often indicates the incomplete removal of the volatile solvent used in 
the manufacture of the oleoresin. 


The flash point may prove useful in the evaluation of an essential oil. 
Unfortunately insufficient data exist to use this property as a criterion of 
quality for normal, unadulterated oils. However, the flash point has value 
as an indication of adulteration: additions of adulterants such as alcohol 
and low boiling mineral spirits will greatly lower the flash point. 

Occasionally it is necessary to determine the flash point of a synthetic, 
solvent, or a mixture because of shipping regulations. 

Several types of instruments are available for the determination; e.g., 
the Pensky-Martin closed tester, 50 the Tag closed tester, 61 the Cleaveland 52 
and the Tag open cup testers. The Tag open cup tester is simple, inexpen- 
sive, and entirely satisfactory for use in the essential oil industry. The 
procedure described below is intended primarily for this instrument (see 
Diagram 4.6). 

Procedure: Fill the metal bath with water of about 60 F. 
(15.6 C.) temperature, 54 leaving room for displacement by the 
glass oil cup which is placed in the water bath. Suspend the 
thermometer in a vertical position so that the bottom of the 
bulb is about J in. from the bottom of the glass cup and so that 

60 A description of the instrument and a detailed procedure for its use may be found in 
A.S.T.M. Designation D93-42. 

A.S.T.M. Designation D5(>-36. 

A.S.T.M. Designation D02-33. 

M This procedure is based on the directions for using the Tag Open Fire Tester supplied 
by the Tagliabue Manufacturing Co., Brooklyn, N. Y. 

64 It is customary in the United States to report flash points in degrees Fahrenheit. 



the thermometer is suspended half way between the center and 
the back of the glass cup. Fill the glass cup with the oil to be 
tested in such a manner that the top of the meniscus is exactly 
at the filling line at room temperature (i.e., J in. from the upper 
edge of the cup). Be sure that there is no oil on the outside of 
the cup or on its upper level edge ; use soft paper to clean the 
cup in preference to a cloth. Remove any air bubbles from the 

DIAGRAM 4.6. Tag open cup tester for the determination of flash point. 

surface of the oil. Adjust the horizontal flashing taper guide 
wire in place. The instrument should stand level and should 
be protected from drafts. It is desirable that the room be dark- 
ened sufficiently so that the flash may be readily discernible. 
Avoid breathing over the surface of the oil. Heat the water 
bath with a small burner so that it will raise the temperature of 
the oil at a rate not faster than 2 F. (1.1 C.) per min. without 
removing the burner during the whole operation. Adjust the 
test flame on the flashing taper so that it is the same size as the 
metal bead mounted on the instrument. Apply this test flame 
to the oil at 5 F. (2.8 C.) intervals: hold the flashing taper 
in a horizontal position and draw it across the guide wire quickly 
and without pause from left to right. (The time of passage of 
the test flame across the cup should be approximately 1 sec.) 
The first or initial flash 55 is called the "flash point." Continue 
heating and testing the oil until the surface ignites and con- 
tinues to burn until quickly blown out with a mouth-open 
breath. This burning point temperature is called the "fire 
test" or "fire point." Repeat the determination and try for a 
flash at the proper trial temperatures indicated in Table 4.8. 

58 The true initial flash should not be confused with a bluish halo that sometimes sur- 
rounds the test flame 



TABLE 4.8. 

(All Temperatures in F.) 

For Oils 
Expected to 
Have a Fire 
Test of 

Try for Flash 

First at 

Then at 










































































Most essential oils contain only small amounts of free acids. Conse- 
quently the acid content is usually reported as an acid number rather than 
as a percentage calculated as a specific acid. 

The acid number of an oil is defined as the number of milligrams of 
potassium hydroxide required to neutralize the free acids in 1 g. of oil. 

In determining the acid number, dilute alkali must be employed since 
many of the esters (e.g., the formates) normally present in essential oils 
are capable of saponification even in the cold in the presence of strong alka- 
lies. Moreover, phenols will react with the alkali hydroxides, making it 
necessary to use special indicators (such as phenol red) for oils containing 
large amounts of phenolic bodies ; this is particularly true in the case of the 

The acid number of an oil often increases as the oil ages, especially if the 
oil is improperly stored; processes such as oxidation of aldehydes and hy- 
drolysis of esters increase the acid number. Oils which have been thor- 
oughly dried and which are protected from air and light show little change 
in the amount of free acids. 

Procedure: Weigh accurately about 2.5 g. of the oil into a 
100 cc. saponification flask. Add 15 cc. of neutral 95 per cent 
alcohol and 3 drops of a 1% phenolphthalein solution. Titrate 
the free acids with a standardized 0.1 N aqueous sodium hy- 
droxide solution, adding the alkali dropvvise at a uniform rate 
of about 30 drops per min. The contents of the flask must be 
continually agitated. The first appearance of a red coloration 
that does not fade within 10 sec. is considered the end point. 


If the determination requires more than 10 cc. of alkali, it should be 
repeated using a 1 g. sample of the oil ; if more than 10 cc. of alkali is still 
required, then a 1 g. sample is titrated with 0.5 N aqueous sodium hydroxide 

The acid number is calculated by means of the following formulas : 

A ., , 5.61 (no. of cc. of 0.1 N NaOH) 

Acid number = - = -= - 

wt. of sample in g. 

= 28.05 (no. of cc. of 0.5 N NaQH) 
wt. of sample in g. 


Acids Molecular Wt. 

Monobasic Acids 

Acetic 60.05 

Anisic 152.14 

Anthranilic 137.13 

Benzoic . ...122.12 

Butyric 88.10 

Capric 172.26 

Caproic 116.16 

Caprylic 144.21 

Cinnamic. . . 148.15 

Formic. . , 46.03 

Furoic 112.08 

Lactic .. 1)0.08 

Laurie 200.31 

Methyl Anthranilic .151.16 

Myristic 228.37 

Oenanthic 130.18 

Oleic 282.46 

Pelargonic 158.24 

Phenylacetic 136.14 

Phenylpropionic 150.17 

Propionic .... 74.08 

Pyruvic . 88.06 

Salicylic ... . . .138.12 

Stearic . . 284.47 

Tiglic 100.11 

Undecylenic 184.27 

Undecylic 186.29 

Valeric 102.13 

Dibasic Adds 

Malonic 104.06 

Phthalic 166.13 

Sebacic 202.25 

Succinic 118.09 

Tartaric 150.09 

Tribasic Acids 

Citric .< - : 192.12 

* All molecular weights have been calculated from the values of the International Atomic 
Weights adopted by ttye Committee on Atomic Weights in 1938. 


For oils containing large amounts of free acid (e.g., orris oil), the free 
icid content may be expressed as a percentage, calculated as a specific acid, 
n such cases it is well to use a 0.5 N alcoholic sodium hydroxide solution. 

Free acid content = 


Free acid content = t/ _- - 

f . v lOOw 


vhcro : m = molecular weight of the acid ; 

a = numlxM* of cc. of 0.5 X alkali used for neutralization; 
b = number of cc. of 0.1 N alkali used for neutralization; 
w = weight of sample in grams. 

If the acid is dibasic, the result must be divided by 2 ; if tribasic, by 3. 
In Table 4.9 arc listed the molecular weights of those acids frequently 
ncountered by the essential oil chemist. 


a. Determination by Saponification with Heat. The determination of 
he ester content is of great importance in the evaluation of many essential 
>ils. Since most esters which occur as normal constituents of essential oils 
ire esters of monobasic acids, the process of saponification may be repre- 
icnted by the following reaction : 


vhere R and II' may be an aliphatic, aromatic, or alicyclic radical (R may 
ilso be a hydrogen atom). 

Procedure: Into a 100 cc. alkali-resistant saponification 
flask weigh accurately about 1.5 g. of the oil. Add 5 cc. of 
neutral 95% alcohol and 3 drops of a 1% alcoholic solution of 
phenolphthalein, and neutralize the free acids \vith standard- 
ized 0.1 N aqueous sodium hydroxide solution. 56 Then add 10 
cc. of 0.5 N alcoholic sodium hydroxide solution, measured ac- 
curately from a pipette or a burette. Attach a glass, air-cooled 
condenser to the flask, 1 m. in length and about 1 cm. in diam- 
eter, and reflux the contents of the flask for 1 hr. on a steam 
bath. Remove and permit to cool at room temperature for 15 
min. Titrate the excess alkali with standardized 0.5 N aqueous 
hydrochloric acid. A further addition of a few drops of phenol- 
phthalein solution may be necessary at tins point. 

** This usually requires not more than 5 drops of the 0.1 N alkali. 



In order to determine the amount of alkali consumed, carry out a blank 
determination, observing the same conditions but omitting the oil. The 
difference in the amounts of acid used in titrating the actual determination 
and the blank gives the amount of alkali used for the saponification of the 
esters. The blank should require an excess of about 100 per cent over the 
amount used in the determination. If insufficient ex- 
cess is used, results will be obtained which are too low. 
It is well to use saponification flasks (see Diagram 
4.7) made of "Jena Glass" or of the special alkali- 
resistant glass recently made available by Corning 
Glass Company. These flasks minimize the amount 
of alkali consumed by the action of the sodium hy- 
droxide on the glass itself. More accurate results are 
thus obtained. This is of importance when the ester 
determination requires more than 1 hr. of refluxing, as, 
for example, in the case of the isovalerates. 

The alcoholic 0.5 N sodium hydroxide solution is 
best prepared by adding 11.5 g. of metallic sodium of 
analytical grade to 1 liter of 95 per cent ethyl alcohol. 
(If larger amounts of solution are to be prepared, use 
43.5 g. of sodium for each gallon of alcohol.) The 
sodium should be added slowly, a few small pieces at a 
time. After weighing out the sodium and cutting it 
into small pieces, it should be protected from atmos- 
pheric moisture until it is used by immersion in low 
boiling petroleum ether. After the required amount 

Saponification flask. 

of sodium has been added, the solution is set aside for several days to 
permit any carbonate to settle; it is filtered into the reagent reservoir and 
permitted to stand for a few days before it is used. A cleur, water white 
solution is thus obtained. The 0.5 N hydrochloric acid may be prepared by 
diluting 85 cc. of concentrated acid to 2 liters; it should then be carefully 

Calculation of Results. The ester content may be calculated from the 
following formula : 

Percentage of ester = T 

where: a = number of cc. of 0.5 N sodium hydroxide used in the saponifica- 


m = molecular weight of the ester ; 
= weight f the sample in grams. 


This formula assumes that the ester is monobasic ; for esters of dibasic 
acids (e.g., dimethyl phthalate) and dihydroxy alcohols (e.g., glycol di- 
acetate), the ester content is divided by 2; for tribasic acids (e.g., triethyl 
citrate) and trihydroxy alcohols (e.g., triacetin), by 3. 67 

The ester may also be expressed by the ester number, which is defined 
as the number of milligrams of potassium hydroxide required to saponify 
the esters present in 1 g. of oil. The use of the ester number is especially 
convenient when the ester present in the oil is unknown, since a knowledge 
of the molecular weight of the ester is not required. 

, , 28.05a 

.bster number = 


Ester numbers are frequently used for oils which contain very small 
amounts of ester; e.g., oil of black pepper and oil of cubeb. A high ester 
number in such cases is usually indicative of adulteration. 

The ester numlx?r may readily l>e converted to an ester content, ex- 
pressed as a weight percentage, by the following formula if the acid radical 
of the ester is monobasic : 

, , . rt\ (ester no.) 

Percentage of ester = 


If the acid is dibasic, the result must be divided by 2; if tribasic, by 3. Also, 
if the alcohol radical contains two hydroxy groups, the result 58 must be 
divided by 2; if three hydroxy groups, by 3. 

In 'Fable 4.10 are listed the molecular weights of those esters which are 
frequently encountered. 

Modification of the General Procedure. Certain esters are not completely 
saponified in a period of 1 hr. by the procedure described above. Notable 
exceptions are the salicy kites which should be rerluxed for 2 hr. ; terpinyl 
acetate, 2 hr. ; menthyl acetate, 2 hr. ; isovalerates, G hr. Certain esters of 
sesquiterpene alcohols require 2 hr. or more e.g., cedryl acetate, 4 hr. A 
solution of potassium hydroxide in a high boiling solvent (such as the mono- 
ethyl ether of ethylene glycol) has been recommended 59 for the determina- 
tion of difficultly saponifiable esters. Such a solution also permits of rapid 
saponification (ca. 15 min.) of other esters. Since such high temperatures 
may have an adverse effect upon some of the constituents of an essential oil, 
this method should be applied with caution. 

67 This is based on the assumption that the ester is neutral in the case of di- and tribasic 
acids, and that all alcoholic groups have been estcrified in the case of esters of di- and tri- 
hydroxy alcohols. 

68 This is based on the assumption that the ester is neutral in the case of di- and tribasic 
acids, and that all alcoholic groups have been esterified in the case of esters of di- and tri- 
hydroxy alcohols. 

69 Steet, Analyst 61 (1936), 687. 





Esters of Monobasic Acids 

Allyl Salicylate 

Amyl Acetate 

Amyl Anisate 

Amyl Benzoate 

Amyl Butyrate 

Amyl Caproate 

Amyl Caprylate . ... 

Amyl Cinnamate 

Amyl Formate 

Amyl Furcate 

Amyl Heptine Carbonate . . 

Amyl Laurate 

Amyl Myristate 

Amyl Oenanthate 

Amyl Phenylacetate 

Amyl Propionate 

Amyl Pyruvate 

Amyl Salicylate 

Amyl Undecylate 

Amyl Undecylenate 

Amyl Valerate 

Anisyl Acetate 

Anisyl Formate 

Benzyl Acetate 

Benzyl Benzoate 

Benzyl Butyrate 

Benzyl Cinnamate 

Benzyl Formate 

Benzyl Heptine Carbonate 

Benzyl Phenylacetate 

Benzyl Propionate 

Benzyl Salicylate . . 

Benzyl Valerate 

Bornyl Acetate 

Butyl Acetate 

Butyl Benzoate 

Butyl Butyrate 

Butyl Formate 

Butyl Furoate 

Butyl Lactate 

Butyl Phenylacetate 

Butyl Propionate 

Butyl Salicylate 

Butyl Stearate 

Butyl Undecylenate 

Butyl Valerate 

Cedryl Acetate 

lar Wt. 




Cinnamyl Acetate 

Cinnamyl Benzoate 

Cinnamyl Butyrate 

Cinnamyl Cinnamate 

Cinnamyl Formate 

Cinnamyl Propionate 

Cinnamyl Valerate 

Citronellyl Acetate 

Citronellyl Benzoate 

Citronellyl Butyrate 

Citronellyl Caproate . . 
Citronellyl Cinnamate. . 

Citronellyl Formate 

Citronellyl Propionate 

Citronellyl Valerate 

Cresyl Acetate 

Cresyl Butyrate. 
Cresyl Cinnamate. . . 
Cresyl Phenylacetate 
Cyclohexanyl Acetate 1 
Cyclohexanyl Butynite 
Decyl Acetate .... 

Decyl Formate 

Dimethyl Benzyl Carbinyl Ace- 

Ethyl Acetate 

Ethyl Amyl Carbinyl Acetate . 

Ethyl Anisate ... 

Ethyl Anthranilate .... 

Ethyl Benzoate .... 

Ethyl Butyrate 

Ethyl Caprate 

Ethyl Caproate 

Ethyl Caprylate . . . 

Ethyl Cinnamate 

Ethyl Dccinc Carbonate . 

Ethyl Formate 

Ethyl Furoate 

Ethyl Heptine Carbonate . . 
Ethyl Hexyl Carbinyl Acetate 

Ethyl Lactate 

Ethyl Methyl Phenyl CUyridate 

Ethyl Myristate 

Ethyl Octirie Carbonate .... 
Ethyl Oenanthate.. 

Ethyl Oleate 

Ethyl Pelargoriate 

Ethyl Phenylacetate 

lar Wt. 



* All molecular weights have been calculated from the values of the International 
Atomic Weights adopted by the Committee on Atomic Weights in 1938. 



TABLE 4.10. Continued 


lar Wt. 


ar Wt. 

Ethyl Propionate ... , 
Ethyl Pyruvate 
Ethyl Salicylate 


Methyl Formate. ... 
Methyl Furoate 
Methyl Heptine Carbonate 
Methyl Laurate 



Ethyl Umlecylate 
Ethyl Undeeylenate . . .... 
Ethyl Valerate 
(icranyl Acetate 
Geranyl Benzoate 
Geranyl Butyrate . 
Geranyl Formate . . . . 
Geranyl Phenylacvtate. . 
Geranyl Propionate. . 
Geranyl Tiglate . . . 
Geranyl Valerate . 
Guaiyl Acetate 
Guaiyl Phenylacetate 
Ilcptyl Acetate 
Heptyl Caproate. . . . 
Heptyl Formate 
Ileptyl Oenanthate 
Heptyl Propionate 
Ileptyl Valerate 
Hexyl Acetate 
Hexyl Butyrate 
Hexyl Formate 
Hexyl Valerate 
Isopulegyl Acetate 
Isopulegyl Formate 
Linalyi Acetate .... 
Linalyl Anthranilate. . 
Linalyi Benzoate . . 
Linalyl Butyrate . . . 
Linalyi Oinnamate 
Linalyl Formate . . 
Linalyl Phenylacetate 

Methyl Methyl Anthranilate. . 
Methyl Mvristate 

Methyl Octine Carbonate. . .. 
Methyl Oenanthate 
Methyl Pelargonate 
Methyl Phenylacetate 
Methyl Phenylpropionatc . . 
Methyl Propionate 

Methyl Salicylate 
Methyl Valrrate . . . 
Neryl Acetate 
Neryl Butyrate. 
Neryl Formate 
Neryl Phenylacetate ... 
Neryl Propionate .... 
Neryl Valerate . . 
Nonyl Acetate 
Nonyl Butyrate 

Nonyl I^actone 
Octyl Acetate . 

Octyl Benzoate. .. . . . 
Octyl Butyrate. . . . 
Octyl Formate 
Octyl Oenanthate. ... ... 
Octyl Propionate. .. . . 
Octyl Valerate 
Phenvl Benzoate . ... 

Phenylethyl Acetate 
Phenylethyl Anthranilate 
Phenylethyl Benzoate 
Phenylethyl Butyrate 
Phenyleth3 r l Cinnamate 

Linalyl Valerate 
Menthyl Acetate . . . 
Menthyl Salicylate. . . 
Menthyl Valerate 

Phenylethyl Dimethyl Carbinyl 

Phenylethyl Formate 
Phenylethyl Phenylacetate . 

Phenvlethyl Propionate 

Methvl Anisate 

Phcnylethyl Salicylate 

Methyl Anthranilate 

Phenylethyl Valerate 
Phenyl Methyl Carbinyl Acetate 
Phenylpropyl Acetate 

Methyl Benzoate . . 

Methyl Butyrate . 
Methyl Cap rate 

Phenylpropyl Butyrate 

Methyl Caproate 

Phenylpropyl Cinnamate 

Methyl Caprylate 

Phenylpropyl Formate 

Methyl Cinnamate 

Phenylpropyl Propionate 

Methyl Oecine Carbonate 

Phenylpropyl Valerate 



TABLE 4.10. Continued 


lar Wt. 


lar Wt. 

Propyl Acetate 


Vetivenyl Butyrate. . . 


Propyl Butyrate 


Vetivenyl Formate 

248 35 

Propyl Formate 

88 10 

Vetivenyl Propionate 


Propyl Propionate 

116 16 

Vetivenyl Valerate 

304 46 

Propyl Vale rate 


Rhodinyl Acetate 


Esters of Dibasic Acids 

Rhodinyl Benzoate 


Diamyl Phthalate 

306 39 

Rhodinyl Butyrate . . 


Dibenzyl Succinato 

298 33 

Rhodinyl Formate 


Di butyl Phthalate 

278 3 1 

Rhodinyl Phenylacetate 


Dibutyl Tartrate 

262 30 

Rhodinyl Propionate 


Diethyl Phthalate 

222 23 

Rhodinyl Vale rate 


Diethyl Malonate 

160 17 

Santalyl Acetate 


Diethyl Sobacate 

258 35 

Terpinyl Acetate 


Diethyl Succinate ... . . 

174 19 

Terpinyl Anthranilate 

273 36 

Dimethyl Malonate 

132 11 

Terpinyl Butyrate 


Dimethyl Phthalate 

194 18 

Terpinyl Cinnamate 


Terpinyl Formate 

182 26 

Esters of Tribfisic Acids 

Terpinyl Propionate 
Terpinyl Valerate 
Thujyl Acetate 


Triethyl Citrate 
Trimethyl Citrate . . 




Esters of Trihydroxi/ Alcohols 

Vetivenyl Acetate .... 




In the case of salicylutcs, benzoates, and phthalates, an addition ot 5 cc 
of water should be made before the ester is heated on the steam bath to pro- 
vent the separation of the sodium salts of the acids during the saponification. 

If the oil contains large amounts of free acids, these should be determined 
separately by the procedure described under "Determination of Acids." 
The saponification number, representing the sum of the acid number and 
the ester number, is then determined for the oil using the general procedure 
described above, except that the free acids are not neutralized before the 
addition of the 0.5 N alkali. 

In the case of oils containing large amounts of esters (e.g., oil of winter- 
green), or esters of low-molecular weight (e.g., methyl formate), or esters of 
dibasic or tribasic acids, it becomes necessary to vary the size of the sample 
and the amount of alkali employed. If 10 cc. of alkali is insufficient, 20 cc. 
may be used. For synthetic esters, it is often necessary to decrease the 
size of the sample ; usually 1 g. (of the pure synthetic) is used and 20 cc. of 
alkali. In the case of esters of low molecular weight or esters of polybasic 
acids, a 0.5 g. sample and 20 cc. of alkali may be required. 

Relatively small samples are also required in the case of certain darkly 
colored oils. It may also be necessary to dilute the saponified oil with 
alcohol in order to ascertain the end point of the titration, and to use a spot- 


plate. The use of thymolphthalein (in place of phenolphthalein as an 
indicator) has been suggested 60 for determinations involving red or brown 
solutions, such as result during the saponification of oleoresins. Thymol- 
phthalein changes from a deep blue to colorless in the range pH 9.3 to 
pH 10.5. 

The determination of the ester content by saponification will not yield 
satisfactory results if the oil contains appreciable amounts of aldehydes, 
unless the aldehydes are removed and the residual oil saponified. 

It has been reported that certain phenols also may interfere with the 
3ster determination. 61 In addition to esters, lactones may be determined 
quantitatively by saponification. 

b. Determination by Saponification in the Cold. As an analytical 
procedure, saponification in the cold is not generally applicable. In most 
^ases, long periods of time are necessary to complete the process; further- 
more, side reactions frequently occur which give rise to inconsistent and 
deceptive results. 

Saponification in the cold has a definite value for the determination of 
those esters which are very easily saponified; this is particularly true for 
certain formates. Thus, cold saponification is used in the analysis of 
geranium oils to determine the amount of "actual formate," since the 
standard procedure for the determination of esters with a reflux period of 
1 hr. saponifies not only the geranyl formate but also other esters including 
geranyl tiglate. 

For the determination of geranyl formate in geranium oils, the following 
procedure has given satisfactory results. 

Procedure: Into a 100 cc. saponification flask, weigh ac- 
curately about 1.5 g. of the oil. Add 5 cc. of neutral alcohol 
and 3 drops of a 1% alcoholic solution of phenolphthalein, and 
neutralize the free acids quickly with standardized 0.1 N aque- 
ous sodium hydroxide solution. Add 10 cc. of 0.5 N alcoholic 
sodium hydroxide solution, measured accurately from a burette 
or pipette, and titrate the excess alkali immediately with stand- 
ardized 0.5 N aqueous hydrochloric acid. Calculate the ester 
content as geranyl formate in the usual manner. 

In the case of pure synthetic formates, it is advisable to add 5 cc. of water 
to the flask in order to dissolve the sodium formate which otherwise may 
precipitate out of solution. 


a. Determination by Acetylation. The alcoholic constituents of an 
essential oil are determined by acetylation; i.e., the oil is acetylized with 

60 Saxl, Chemist-Analyst 32 (1943), 11. 

61 Gildemeistcr and Hoffmann, "Die atherischen Ole," 3d Ed., Vol. I, 797. 


acetic anhydride and the ester content of the resulting oil is determined ; from 
this value the percentage of alcohol in the original oil may be calculated. 
The basic chemical processes involved in this determination may be 
summarized by the following equations : 

HI) / Rll 

R2 C OH + O - R2 COOCCHa + CH 3 COOH 
R3J \ R3J 

O=CCH 3 

Rl] Rll 

R2 COOCCH 3 + NaOH - R2 COH + CH 3 COONa 

R3J R3J 

where Rl, R2 and R3 may be a hydrogen atom, an aliphatic, aromatic or 
alicyclic radical. 

For this determination, a special acetylation flask of approximately 100 
cc. capacity is employed. This flask is equipped with an air-cooled con- 
denser attached to the flask by means of a ground glass joint (see Diagram 
4.8). A condenser 1 m. in length is to be preferred in order to prevent the 
loss of volatile constituents. 

Procedure: Introduce into a 100 cc. acetylation flask 10 cc. of 
the oil (measured from a graduated cylinder), 10 cc. of acetic 
anhydride (similarly measured) and 2.0 g. of anhydrous sodium 
acetate. Attach the air condenser, and boil the contents of the 
flask gently for exactly 1 hr. on a sand bath suitably heated by 
an open Bunsen flame or an electric hot-plate. Permit the 
flask to cool for 15 min. and introduce 50 cc. of distilled water 
through the top of the condenser. Heat the flask on a steam 
bath for 15 min. with frequent shaking to destroy the excess of 
acetic anhydride. Transfer the contents of the flask to a 
separatory funnel and rinse the flask with two 10 cc. portions of 
distilled water; add these rinsings to the separatory funnel. 
Shake thoroughly to assure good contact of the aqueous layer 
with the oil. When the liquids have separated completely, 
reject the aqueous layer and wash the remaining oil repeatedly 
with 100 cc. portions of saturated salt solution, until the wash- 
ings are neutral to litmus ; this usually requires three washings. 
Dry the resulting oil with anhydrous sodium sulfate and filter. 
(If the oil has been washed properly, not more than 0.2 cc. of 
0.1 N aqueous sodium hydroxide solution should be required 
per gram of acetylized oil in order to neutralize the remaining 
trace of acetic acid.) 

Saponify the acetylized-oil, using the procedure described under "The 
Determination of Esters," p. 265. 


In order to secure accurate and reproducible results it is important to use 
exactly 2.0 g. of sodium acetate and to reflux the mixture for exactly 1 hr. 
A notable exception occurs in the case of citronella oils, which require a 
reflux period of 2 hr. 

Calculation of Results. If the original oil contains a negligible quantity 
of saponifiable constituents, the free alcohol may be calculated by the follow- 
ing formula : 

Percentage of alcohol in the original oil = ^/w _ ft 091 

where: a = number of cc. of 0.5 N sodium hydroxide solution required for 

the saponification of the acetylized oil ; 

s = weight of acetylized oil in grams used in the saponification ; 
m molecular weight of the alcohol. 

For oils which have not been thoroughly investigated 
and whose alcoholic constituents are not well known, it is 
frequently more convenient to report the result as an ester 
number after acetylation. 

Ester number after acetylation = ' - 


The ester number after acetylation is numerically equal to 
the number of milligrams of potassium hydroxide required 
to saponify the esters present in 1 g. of the acetylized oil. 

If the original oil contains an appreciable amount of 
esters (as indicated by the ester number), the percentage 
of free alcohol may be estimated by the following formula: 

Percentage of free alcohol in the original oil 


501.04 - 0.42d 

where d = (ester number after acetylation ester number) . 
Although this expression is not mathematically precise, 
nevertheless it is sufficiently accurate for all practical work Acetylation flask 
and has been used traditionally by essential oil chemists. 

For the evaluation of essential oils, it is often desirable to know the per- 
centage of total alcohol ; i.e., the percentage of free alcohol plus the percent- 
age of alcohol combined as ester present in the original unacetylized oil. 

Percentage of total alcohol in 
the original oil 

- 0.021a) 


100(w + 42.04) 

where e = ester content in per cent. This formula assumes that all of the 
esterified alcohol present in the original oil is combined as the acetate. 


All formulas in this chapter that calculate the result of an acetylation as a 
percentage actually refer to all constituents which are capable of acetylation 
under the experimental conditions, calculated as a specific alcohol. Thus for 
example, the "total alcohol" in citronella oils includes not only the geraniol, 
free and as ester, but also all other acetylizable constituents and their esters, 
such as, borneol, citronellol, sesquiterpene alcohols, and the aldehyde citronel- 
lal, all calculated as geraniol. These formulas further assume that the alcohol 
is a monohydroxy compound. Table 4.11 gives the molecular weights of 
alcohols frequently encountered in the analysis of essential oils. 


Alcohols Molecular Wt. 

Amyrol 222.36 

Anisyl Alcohol 138.16 

Benzyl Alcohol 108.13 

Borneol 154.25 

Cedrenol 220.34 

Cedrol 222.36 

Cinnamyl Alcohol 134.17 

Citronellol 156.26 

Costol 220.34 

Cyclohexanol 100.16 

Decyl Alcohol 158.28 

Duodecyl Alcohol 186.33 

Elemol 222.36 

Farnesol 222.36 

Fenchyl Alcohol 154.25 

Geraniol 154.25 

Guaiol 222.36 

Isoborneol 154.25 

Isopulegol 154.25 

Linalool 154.25 

Menthol 156.26 

Nerol 154.25 

Nerolidol 222.36 

Nonyl Alcohol 144.25 

Octyl Alcohol 130.23 

Phenylethyl Alcohol 122.16 

Phenylpropyl Alcohol 136.19 

Rhodinol 156.26 

Santalol 220.34 

Terpineol 154.25 

Thujyl Alcohol 154.25 

Undecyl Alcohol 172.30 

Vetivenol 220.34 

* All molecular weights have been calculated from the values of the International 
Atomic Weights adopted by the Committee on Atomic Weight? in 1938. 

Limitations and Modifications of the General Procedure. As mentioned 
above, acetic anhydride employed under the experimental conditions de- 
scribed in the "Procedure" will react with certain compounds found in 


essential oils other than alcohols. Phenols will be quantitatively converted 
into the acetates. Certain aldehydes and ketones are partially acetylated 
and partially destroyed, or are converted to other compounds which are 
capable of acetylation. 

Furthermore, some tertiary alcohols are not quantitatively converted to 
the acetate by this process of acetylation; the most important alcohols in 
this class are terpineol and linalool. 

b. Determination of Primary Alcohols. Phthalic anhydride reacts with 
primary alcohols forming an acid phthalic ester. 

O O 



/ \ / 

RCH 2 OH + CJI 4 O > C 8 H 4 

\ / \ 



O O 

Under the experimental conditions described below, this reaction takes 
place readily at a temperature of about 100 in the case of primary alcohols ; 
for secondary alcohols, the time required for reflux is greatly increased ; for 
tertiary alcohols, no appreciable reaction occurs. 

It is important that the phthalic anhydride does not contain free phthalic 
acid. This may be ascertained conveniently by shaking 1 g. of the an- 
hydride with 10 cc. of benzene and warming to 40 ; a clear solution indicates 
the absence of appreciable amounts of phthalic acid. 

Procedure: 62 Into a 100 cc. acetylation flask introduce about 
2 g. of powdered phthalic anhydride, accurately weighed, and 
about 2 g. of the oil, accurately weighed. Add 2 cc. of benzene, 
measured from a graduated cylinder. Heat the flask on a steam 
bath with frequent shaking for 2 hr. Then permit the flask to 
cool for 30 min. Add 60 cc. of 0.5 N aqueous potassium hy- 
droxide solution, accurately measured from a pipette or burette. 
Stopper the acetylation flask with a ground glass stopper and 
shake thoroughly for 10 min. Titrate the excess of alkali with 
standardized 0.5 N hydrochloric acid, using 3 drops of a 1 per 
cent phenolphthalein solution as indicator. 

Run a blank determination omitting the oil, and from this 
calculate the amount of alkali which would be required for the 
weight of phthalic anhydride used in the actual determination. 

Calculate the percentage of primary alcohol by the following 
formula : 

, . t , , fo(6 - a) 

Percentage of primary alcohol 

" Ber. SchimmeL & Co., October (1912), 39. 


where : m = the molecular weight of the primary alcohol ; 

b = the calculated number of cc. of 0.5 N potassium 
hydroxide required for the amount of phthalic an- 
hydride used in the determination ; 

a = the number of cc. of 0.5 N potassium hydroxide 
consumed in the determination; 

w = weight of oil in grams. 

c. Determination of Tertiary Terpene Alcohols. Most tertiary alcohols 
suffer partial or complete breakdown and dehydration when treated with 
acetic anhydride. In the event that an oil contains a large percentage of 
such easily dehydrated alcohols, special techniques are required. 

/. The Method of Glichitch. The Glichitch method of formylation for 
the estimation of easily dehydrated alcohols has been successfully employed 
for the determination of linalool and terpineol. 

Procedure: Introduce 15 cc. of aceto-formic acid reagent in a 
125 cc. glass-stoppered Krlenmeyer flask. Cool in an ice bath 
and add slowly 10 cc. of the oil to be tested. Allow the mixture 
to stand for not less than 72 hr. at room temperature. The ice 
in the bath should not be renewed. At the end of this interval 
pour the contents of the flask into a separatory funnel. Shake 
well with 50 cc. of ice cold water and allow to stand for 2 hr. 
Separate the oil and wash successively with 50 cc. of cold water, 
50 cc. of a 5% sodium bicarbonate solution, and then with two 
50 cc. portions of water. Separate the oil and dry with an- 
hydrous sodium sulfate. Filter and saponify by refluxing with 
0.5 N alcoholic sodium hydroxide. Calculate the alcohols in the 
usual way on the assumption that they are present as formates. 

Preparation of the Aceto-Formic Reagent. To 2 volumes of 
acetic anhydride, previously cooled to at least 0, add slowly 1 
volume of 100 per cent formic acid. 64 Mix thoroughly and then 
heat to 50 for 15 minutes and immediately cool in an ice bath. 

II. The Method of Boulez. 65 The Boulez method of acetylation makes 
use of a diluent in order to lessen the dehydrating effect of acetic anhydride. 
The period of acetylation, however, must be prolonged. This gives satis- 
factory results for linalool and terpineol if the prescribed conditions are 
rigidly followed. 

The original method suggested oil of turpentine as a diluent in the ratio 

of 1 part of the oil under examination to 5 parts of oil of turpentine. 66 The 


** Bull, soc. chim. [4] 33 (1923), 1284. 

64 It is very important to use a highly purified formic acid of substantially 100 per cent 
strength. The usual A.R. grade of formic acid (specific gravity = 1.20; HCOOH = ap- 
proximately 87 per cent) is useless for the preparation of this reagent. 

65 Butt. soc. chim. [4] 1 (1907), 117. 

66 Boulez later suggested an even greater dilution namely, 1 g. oil to 25 cc. of xylene. 
Butt. soc. chim. [4] 35 (1924), 419. 


chemists of Schimmel & Company 67 modified the procedure by substituting 
xylcne as a diluent in the ratio of 1:4. The period of acetylation is very 
important ; for terpineol 5 hr. are required, longer or shorter periods give 
low values ; for linalool, 7 hr. 

This modified procedure gives reproducible data. Great care must be 
exercised during this determination since any error introduced will be multi- 
plied by 5 in the final result. 

///. Dehydration Methods. Dehydration methods are based upon the 
catalytic decomposition of tertiary alcohols and the splitting off of water. 
The amount of water obtained is determined from which the percentage of 
tertiary alcohol may be calculated. 

Such a method has been described by Ikeda and Takeda, 68 using zinc 
chloride. A very satisfactory dehydration catalyst is iodine. Additions 
of approximately 0.5 per cent of catalyst to the oil will prove sufficient. 
Such dehydration methods offer the advantage that only tertiary alcohols 
are determined, primary and secondary alcohol being unaffected. This is 
an advantage not found in the other methods described here. Hydroxy 
ketones and hydroxy aldehydes will interfere in this procedure, since both 
split off water under the experimental conditions. 

A convenient method for the determination makes use of the distillation 
trap of Sterling and Bid well. 

Procedure: Dry the oil thoroughly by permitting it to stand 
overnight in contact with anhydrous sodium sulfate. Into 
a 1 liter, round bottom flask, introduce a sufficiently large sam- 
ple, accurately weighed, to yield about 5 cc. of water upon de- 
hydration of the tertiary alcohol. Add 0.5% of solid iodine 
as catalyst and 500 cc. of xylene. Connect the flask to a stand- 
ard Sterling and Bidwell water-trap; attach a water-cooled, 
straight tube condenser. Heat the flask by means of an oil 
hath. Proceed as in the "Determination of Water Content," 
p. 323. Measure the amount of collected water and calculate 
the percentage of tertiary alcohol. 

This method docs not yield highly accurate results, but is a convenient 
method for the determination of the tertiary alcohol content. 

IV. Acctyl Chloride- Dimethyl Aniline Method. This method, originally 
described by Fiore, 69 gives exceptionally concordant and satisfactory results 
in the case of linalool and linalool-containing oils. It has been carefully 
evaluated by the members of the Essential Oil Association of the U. S. A. 
and adopted by that body. Preliminary experiments with terpineol and 

07 Ber. Schimmel & Co., April (1907), 128. 

J. Chem. Soc. Japan 57 (1936), 442. Chem. Abstracts 30 (1936), 5907. 

89 News Capsule (Essential Oil Association of U.S.A.), Vol. 1, No. 15 (1943). 


other tertiary terpene alcohols indicate that this may prove to be a valuable 
method for many tertiary alcohols. 

The method is described below in the final form in which it was accepted 
by the Essential Oil Association for the determination of linalool. 

Procedure: Ten cc. of linalool or essential oil containing 
linalool, previously dried with sodium sulfate, is introduced into 
a 125 cc. glass-stoppered Erienmeyer flask cooled with ice and 
water. To the cooled oil is added 20 cc. dimethyl aniline 
(monomethyl free) and the contents thoroughly mixed, then 
8 cc. acetyl chloride (reagent grade) and 5 cc. of acetic anhydride 
are added, the anhydride serving as a solvent to prevent crystal- 
lization of the reaction mass. The mixture is cooled for a fe*v 
minutes and permitted to stand at room temperature for one- 
half hour after which time the flask is immersed in a water bath 
maintained at 40 C. 1 for three hours. At the end of this 
time the acetylated oil is washed three times with 75 cc. of ice 
water, then with successive washes of 25 cc. of 5% sulfuric acid 
until the separated acid layer fails to liberate any dimethyl 
aniline with an excess of caustic. After removal of the di- 
methyl aniline, the acetylated oil is washed with 10 cc. of 10% 
sodium carbonate solution and then finally washed neutral with 

The oil is separated, dried over anhydrous sodium sulfate 
and the ester number determined in the usual manner. The 
linalool content can thus be obtained directly from saponifica- 
tion tables or by substitution in the following formula : 

,,.,.., cc. AV2KOHX 154.14 

Percentage of linalool = ; 

20 (wt. sample-cc. N/2 KOHX0.021) 

As this test is further to be used for other oils containing 
linalool, besides linalool itself, a correction factor is necessary 
with oils containing significant amount of esters. For such oils, 
the following standard formula is recommended : 

Percentage of total linalool = jvX U ~ ( E X0.0021)) 

& ^ 

where: A ~ cc. half normal alkali required for saponification ; 
B = weight of sample ; 

E = per cent of esters calculated as linalyl acetate in the 
original oil. 

d. Determination of Citronellol by Formylation. Most terpene alcohols 
are dehydrated by strong formic acid, giving rise to nonsaponifiable terpenes. 
A notable exception is citronellol which is converted almost quantitatively to 
the corresponding formate. This results in a convenient and satisfactory 
method for the determination of citronellol in the presence of geraniol and 


Formylation has become a standard procedure for the determination of 
citronellol in rose oils. The procedure to be followed is identical to that 
described under " Determination by Acetylation," p. 272, with the exception 
that the 10 cc. of acetic anhydride is replaced with 20 cc. of 100 per cent 
formic acid, and the anhydrous sodium acetate is omitted. 

Place in the flask short pieces of glass tubing to permit heat transfer 
throughout the mixture. This is particularly important if the oil contains 
a high percentage of geraniol, since the dehydration which results may dilute 
the formic acid sufficiently to cause the formation of two layers in the flask. 
Should this occur, there will be some danger of the lower layer becoming 
overheated and violently throwing out the contents of the flask through the 
air condenser. A small clay chip should also be placed in the flask to help 
prevent such overheating. 

The percentage of alcohol (citronellol) in the original oil may be calcu- 
lated from the amount of alkali consumed in the subsequent saponification. 

Percentage of alcohol in the original oil = 

_ ^ ^ . . 

where : a = number of cc. of 0.5 N sodium hydroxide solution required for 

the saponification of the formylated oil ; 
m = molecular weight of the alcohol ; 
s = weight of formylated oil in grams. 


Of the many procedures which have been suggested for the determination 
of aldehydes and ketones, only four general methods have attained practical 
significance. These are the bisulfite method, the neutral sulfite method, the 
phenylhydrazine method, and the hydroxylamine methods. 

a. Bisulfite Method. The bisulfite method is an absorption process 
based upon the general reaction : 70 


RCHO + NaHSO 3 - > RCH 

S0 8 Na 

Upon shaking a measured quantity of oil with a hot aqueous solution of 
sodium bisulfite, an addition compound 71 forms which is generally water 
soluble and which dissolves in the hot bisulfite solution; the nonaldehyde 

70 There exists some question as to the linkage of the SO$Na group to the C atom of 
the carbonyl group ; this linkage may occur through the S atom or possibly through the 
O atom. 

71 In many cases, this addition compound is a water soluble sulfonate instead of (or in 
addition to) the normal bisulfite addition compound of the carbonyl group. See p. 282. 



9mm." 1 

Approximate Volume 

150 cc 

100 cc. 

portion of the oil separates as an oily layer which can be measured con- 
veniently in the graduated neck of a cassia flask. 

These special flasks have been known traditionally as cassia flasks be- 
cause they were first used for the determination of the cinnamic aldehyde 
content of cassia oil. They have a large bulbous body with a long thin 
neck graduated in divisions of 0. 1 cc. The two types (having the dimensions 
shown in Diagram 4.9) have proved most useful in the laboratory. The 

larger flask with a capacity of 150 
cc. and a thin neck graduated to 
contain 6 cc. is very satisfactory 
for the determination of alde- 
hydes and ketones. The smaller 
flask with a capacity of 100 cc. 
and a neck graduated to contain 
10 cc. may also be used for such 
determinations, although the ac- 
curacy will suffer somewhat. 
Furthermore, the capacity of 
these smaller flasks does not per- 
J- mit as thorough and as intimate 
contact of the oil and solution 


vp when the flask is shaken ; if such 

Y i \ / ; ' ^ <<-H i- a flask is used, the shaking 

| -7cm. H h--6cm.-->| should be thorough and pro- 

DIAGRAM 4.9. Cassia flasks. longed. In general, the use of 

these smaller flasks is not recom- 
mended for the determination of aldehydes and ketones, unless the oil 
contains less than 40 per cent of reactive carbonyl compounds. 

The bisulfite method is perhaps the most convenient and simple of the 
four general methods. As such, it is frequently used in the trade because 
it requires no standardized solutions, analytical balance, or special skill. 

This method has proved satisfactory for the estimation of cinnamic alde- 
hyde in cassia oil, of benzaldehyde in bitter almond oil, of citronellal in 
Eucalyptus citriodora oil ; it is the commercially accepted method for the de- 
termination of citral in lemongrass oil. 72 

The bisulfite method suffers from certain disadvantages inherent in the 
absorption process. Water-soluble adulterants analyze as apparent alde- 
hyde. The time required for a determination is usually at least I hr. The 

72 The neutral sulfite method gives a more accurate value of the true citral content; in 
addition to citral, the bisulfite method determines other carbonyl constituents which occur 
as natural constituents of lemongrass oils (e.g., part of the methyl heptenone). The values 
obtained by the bisulfite method are generally about 4 per cent higher than those obtained 
by the neutral sulfite method for the normal lemongrass oils of commerce. 


results obtained are volume percentages. These methods are applicable 
only to oils containing large amounts of aldehydes or ketones. Water- 
soluble sulfonates may be formed from noncarbonyl compounds having 
double bonds; these will interfere with the accuracy of the analytical 
results. 73 

The bisulfite method suffers from further disadvantages. There is no 
definite indication when all of the aldehyde has completely reacted. Al- 
though satisfactory for most aldehydes, the method is not suitable for the. 
determination of such ketones as carvone, thujone, pulcgone, menthone, 
fenchone, or camphor. 

Procedure: 74 Into a 150 cc. cassia flask, having a thin neck 
graduated in 0.1 cc. divisions, introduce 75 cc. of a freshly pre- 
pared, saturated, aqueous solution of sodium bisulfite, 75 meas- 
ured from a graduated cylinder. Pipette exactly 10 cc. of the 
oil into the flask. Upon thorough shaking, a semisolid mass 
frequently will result. Immerse the flask in a beaker of boiling 
water and occasionally shake until the solid addition compound 
has gone completely into solution. Shake the flask repeatedly 
to assure complete reaction of the aldehyde with the bisulfite 
solution. A further addition of 25 cc. of bisulfite solution is 
made, and the flask is again repeatedly shaken. After standing 
undisturbed in the beaker of boiling water for 10 min. to permit 
the unreacted oil to rise to the surface, add sufficient sodium bi- 
sulfite solution to force the unreacted oil into the neck of the 
flask. Any droplets of oil adhering to the sides are made to rise 
into the neck by gently tapping the flask, and by rotating it 
rapidly between the palms of the hands. After cooling the 
flask to room temperature, measure the amount of unreacted oil. 
The aldehyde content may then be calculated by means of the 
following; formula : 

Percentage of aldehyde = 10(10 no. of cc. of unreacted oil). 

As mentioned above, this result is a volume percentage. It may be 
converted into a weight percentage if the specific gravity of the original 

73 In this connection, sec Dodge, Am. Perfumer, May (1940), 41. According to this 
authority only small amounts of unsaturatcd alcohols will dissolve if the solution of NaHSOs 
is stronger than molar (10.4 per cent). 

74 Variations of this procedure have been suggested by other authorities. Gildemeister 
and Hoffmann ("Die atherischen Ole," 3d Ed., Vol. I, 739) suggest the use of a 30 per cent 
aqueous solution of sodium acid sulfite which does not contain too much free sulfurous acid; 
if necessary the solution should be neutralized with sodium carbonate. It has been the 
experience of the laboratories of Fritzsche Brothers, Inc., that a freshly prepared solution 
of NaHSOs made with Analytical Grade of reagent does not contain sufficient free II^Oj 
to interfere with the reaction ; the separation of the noncarbonyl portion of the oil is sharper 
and more complete if a saturated solution of NaHSOj is employed instead of a 30 per cent 

76 At room temperature, this will be approximately a 40 per cent (wt./vol.) solution. 


oil and of the aldehyde is known : 

, , .,, //>/ , i N / dJJ* of aldehyde or ketone \ 
Percentage by weight = (% by volume) ( d 16 of oil J 

After cooling to room temperature, a small amount of the bisulfite add 
tion compound will often precipitate out of solution, sometimes forming a 
the surface where the oil and aqueous layers meet; this renders an exac 
reading difficult. The addition of a few drops of water (added with 
medicine dropper in such a way that the water runs down along the insid 
of the neck of the flask), which will remain temporarily on top of the bisu 
fite solution, gives a sharp separation of the oil and aqueous layers. If th 
oil contains heavy metals, these should be removed before the determinatio 
by shaking the oil thoroughly with a small amount (about 1 per cent) < 
powdered tartaric acid and filtering; a sharper separation of the noncai 
bonyl layer will then result. 

The procedure described above will prove satisfactory for those aide 
hydes which form water-soluble sulfonates in addition to the normal bisulfit 
addition compound e.g., citral, citronellal, 76 cinnamic aldehyde. 

For aldehydes which form only the normal addition compound (e.g 
compounds which have no double bonds other than those present in th 
carbonyl group or benzene ring) but which form water-soluble bisulfite add 
tion compounds, the procedure must be modified. For the determination c 
phenylpropyl aldehyde, 77 benzaldehyde, 78 and anisic aldehyde, use a 10 c< 
sample and only 50 cc. of the saturated bisulfite solution. The norm* 
addition compound which forms usually will not dissolve in the saturate 
bisulfite solution even after heating; consequently the flask should be fille 
by the addition of 25 cc. portions of water 19 (instead of bisulfite solution 
After each addition, the flask should be thoroughly shaken and then in 
mersed in the boiling water for a period of about 5 min. The additio 
compound slowly dissolves and the nonreacting oily layer is driven into th 
neck of the flask and measured. Upon cooling and standing, some of th 

76 In the determination of citronellal, the addition compound will often separate upc 
cooling; hence the reading should be taken as soon as the neck of the flask has cooled 1 
room temperature. 

77 In the determination of phenylpropyl aldehyde, considerable amounts of the additic 
compound separate upon cooling; however, a reading is possible. 

78 Use is made of the poor solubility of the benzaldehyde addition compound in saturab 
NaHSOs solution for the detection of benzaldehyde in cinnamic aldehyde; cinnamic aid 
hyde forms a sulfonate which dissolves completely in saturated NaHSOj solution. Henc 
the separation of a solid addition compound upon cooling the contents of the flask to rooi 
temperature is indicative of the presence of benzaldehyde. 

79 Gildemeister and Hoffmann ("Die atherischen Ole," 3d Ed., Vol. I, 740) also recor 
mend additions of water instead of NaHSOj solution for the determination of benzald 
hyde, anisic aldehyde, and phenylacetaldehyde. 


addition compound may settle out of solution. However, a reading usually 
may be obtained. 

In general, this modified procedure will not be satisfactory for the de- 
termination of decyl aldehyde, 80 cuminic aldehyde, 81 methyl heptenone, 82 or 
phenylacetaldehyde which has polymerized. 83 

b. Neutral Sulfite Method. This is also an absorption method. Using 
a neutral sufite solution, sodium hydroxide is liberated as the reaction pro- 
ceeds ; this must be periodically neutralized with acid to permit the reac- 
tion 84 to go to completion. 


RCHO + Na 2 SO 3 + H 2 O RCH + NaOH 

S0 3 Na 

Although this method suffers from the disadvantages of an absorption 
process, nevertheless it offers certain advantages over the use of the bisulfite 
technique. Through the use of phenolphthalein, the exact end point of 
the reaction may be determined. Furthermore, some ketones react with 
neutral sulfite completely, so that this method may be used for their de- 
termination; this is specifically of importance for the determination of 
carvone in spearmint, dill, and caraway oils, of pulegone in pennyroyal oil, 
and of piperitone in eucalyptus oils. Carvone reacts smoothly requiring 
about 1 hr. for the determination The reaction with piperitone and with 
pulegone is very slow : only a 5 cc. sample should be used and the flask should 
be heated in a bath of vigorously boiling water. 

Procedure: Into a 150 cc. cassia flask, having a thin neck 
graduated in 0.1 cc. divisions, introduce 75 cc. of a freshly pre- 
pared, saturated, aqueous solution 85 of sodium sulfite, measured 
from a graduated cylinder. Add a few drops of a 1 per cent 
alcoholic phenolphthalein solution and neutralize the free alkali 
with a 50 per cent (by volume) aqueous acetic acid solution. 
Then pipette exactly 10 cc. of the oil into the flask and shake 
thoroughly. Immerse the flask in a beaker of boiling water and 
shake repeatedly. Neutralize the mixture from time to time 

80 Upon cooling, the entire contents of the flask will solidify making a reading difficult. 

"The addition compound formed is not sufficiently soluble even when the flask is 

82 The reaction with methyl heptenone is incomplete under the condition of the de- 

M The nonaldehyde portion settles to the bottom of the flask. Reclaire (Perfumery 
Essential Oil Record 12 (1921), 341) recommends the use of a special flask for this determina- 
tion. The hydroxylamine method (see p. 285) will prove entirely satisfactory. 

M See footnotes 71 and 72, p. 279. 

86 At room temperature this will be approximately a 30 per cent (wt./vol.) solution. 


with the 50 per cent acetic acid. 86 Continue this procedure 
until no further pink color appears upon the addition of a few 
more drops of phenolphthalein solution. Permit the flask to 
remain in the boiling water for an additional 15 min. to assure 
complete reaction. Then add sufficient neutralized sodium 
sulfite solution to raise the lower limit of the oily layer within 
the graduated portion of the neck. Any droplets of oil adhering 
to the sides are made to rise into the neck by gently tapping the 
flask, and by rotating it rapidly between the palms of the hands. 
After cooling the flask to room temperature, measure the 
amount of unreacted oil. The aldehyde content may then be 
calculated by means of the formula given under bisulfite method. 

The neutral sulfite method is the official method of "The United States 
Pharmacopoeia" for the determination of cinnamic aldehyde in cassia oil, 87 
for carvone in spearmint oil, 88 and of "The National Formulary" for carvone 
in caraway oil. 89 It proves satisfactory for the determination of citral in 
lemongrass oils, 90 the reaction being very rapid. 

As in the case of the bisulfite method, oils containing heavy metals 
should be treated with tartaric acid before a determination is attempted 
(see p. 311). 

c. Phenylhydrazine Method. The phenylhydrazine method is seldom 
used today. It attained importance as the first practical method for the 
assay of citral in lemon oil. 91 The official method of "The United States 
Pharmacopoeia," Tenth Revision, is included here, since commercial con- 
tracts occasionally specify that aldehydes be determined by the phenyl- 
hydrazine method. 

An accurately measured amount of an alcoholic solution of freshly dis- 
tilled phenylhydrazine is added to a weighed amount of the oil. The excess 
of phenylhydrazine is titrated with hydrochloric acid. A blank is run 
simultaneously, and from the difference in the amounts of standardized 
hydrochloric acid required for the blank and the determination, the per- 
centage of aldehyde is calculated. 

RCHO + C 6 H 6 NNH 2 -> C 6 H 6 NX = CIIR + H 2 O 

86 "The United States Pharmacopoeia," Thirteenth Rev., 132, suggests neutralization 
with a 30 per cent NaHSO 3 solution. However, the volume of solution frequently be- 
comes too great to permit thorough shaking. 

87 Thirteenth Revision, 132. 

88 Thirteenth Revision, 510. 

89 Eighth Edition, 121. 

90 See footnote 72, p. 280. 

91 This method was first proposed by Kleber, Am. Perfumer 6 (1912), 284. 


The method, as described, is suitable for the determination of aldehydes 
in the citrus oils. 

Procedure:** Place about 15 cc. of oil of lemon in a tared, 
250 cc. Erlenmeyer. flask, and weigh accurately. Add 10 cc. of 
an alcoholic solution of phenylhydrazine 93 (1 in 10) (not darker 
in color than pale yellow), and allow it to stand for 30 min. at 
room temperature. Then add 3 drops of a 0.1% aqueous solu- 
tion of methyl orange, and neutralize the liquid by the addition 
of half-normal hydrochloric acid. If difficulty is experienced in 
determining the end point of the reaction, continue the titration 
until the liquid is distinctly acid, transfer it to a separatory 
funnel, and after the layers have separated draw off the alcoholic 
portion. Wash the oil remaining in the funnel with distilled 
water, adding the washings to the alcoholic solution, and titrate 
the latter with half-normal sodium hydroxide. Carry out a 
blank test identical with the foregoing, omitting the oil of lemon, 
and note the amount of half-normal hydrochloric acid consumed. 
Subtract the number of cc. of half-normal sodium hydroxide 
from the number of cc. of half-normal hydrochloric acid con- 
sumed in the test containing the oil of lemon, and this result 
from the number of cc. of half-normal hydrochloric acid con- 
sumed in the test without the oil of lemon. Each cc. of this 
difference corresponds to 0.07609 g. of aldehydes calculated as 

In the case of orange oils, the aldehyde is usually calculated as decyl ; the 
factor then used is 0.07813. In the case of grapefruit oils, the aldehydes are 
frequently calculated as an equal mixture of octyl and decyl; the factor 
then used is 0.07 112. 

The results obtained in the above method represent percentages by 

d. Hydroxylamine Methods. Two important techniques have been 
developed, both based upon the use of hydroxylamine for the determination 
of aldehydes and ketones. The first makes use of a solution of hydroxyl- 
amine hydrochloride and the subsequent neutralization with standard- 
ized alkali of the hydrochloric acid liberated by the reaction. The second 
technique makes use of a solution of hydroxylamine (i.e., a solution of the 
hydrochloride with substantially all of the combined hydrochloric acid 
previously neutralized with alkali) ; after the reaction with the aldehyde or 
ketone, the mixture is titrated with standardized acid. The latter proce- 
dure is known as the Stillman-Reed method. Both modifications are based 

92 "The United States Pharmacopoeia," Tenth Revision, 260. 

93 The phenylhydrazine solution should be measured accurately from a pipette or 


upon the fundamental reaction : 

RCHO + NH 2 OH-HC1 RCH=NOH + H 2 O + HC1 

R R 

C=O + NH 2 OH-HC1 > C=NOH + H 2 + HC1 

R/ R/ 

The hydroxylamine methods offer many advantages over the absorption 
processes. Relatively small amounts of the oil are required for a determina- 
tion. The reaction of hydroxylamine with aldehydes is rapid, shortening 
the time required for a determination. Water-soluble adulterants which do 
not contain a carbonyl group do not analyze as apparent aldehyde or ketone. 
The methods have proved satisfactory for the determination of certain 
ketones (such as menthone and thujone) which cannot be determined con- 
veniently by the absorption procedures. In fact, hydroxylamine will react 
with practically all aldehydes and most ketones encountered by the essential 
oil chemist. Furthermore, these hydroxylamine methods prove excep- 
tionally applicable to oils which contain only small amounts of aldehydes or 
ketones (e.g., lemon oils), and to oils containing large amounts of free acids 
(e.g., orris oils). The solutions used for the standard procedure are stable 
and can be kept for many months; however, the Stillman-Reed solution 
deteriorates rapidly and is best prepared when needed. 

The hydroxylamine methods have certain disadvantages not inherent 
in absorption techniques. It must be remembered that the calculation of 
results involves the molecular weight of the aldehyde or ketone, giving 
percentages by weight; hence adulterations with carbonyl compounds of 
lower molecular weight give apparent percentages which are too high. 
If more than one aldehyde or ketone is present in an oil, all are calculated 
as a specific carbonyl compound. Since the reaction of hydroxylamine 
is quite universal, it is difficult to determine an individual component. 
Nor can the carbonyl and noncarbonyl portions be separated conveniently 
and studied individually. 

Standard Procedure: 9 * Into a 100 cc. saponification flask 
weigh accurately the requisite amount of oil or synthetic and 
add 35 cc. of 0.5 N hydroxylamine hydrochioride solution, 
measured from a graduated cylinder. Permit the flask to stand 
at room temperature for the proper length of time and titrate 
the liberated hydrochloric acid with standardized 3.5 N alcoholic 
sodium hydroxide. The titration is continued until the original 
greenish shade of the hydroxylamine solution is obtained. A 

94 This is essentially the procedure described in "The United States Pharmacopoeia," 
Twelfth Revision, 314, for the determination of benzaldehyde in bitter almond oil. 


second flask containing 35 cc. of hydroxylamine hydrochloride 
solution may be used as a blank to assure a more accurate color 
match. 96 

Percentage of aldehyde or ketone = 


where : a = number of cc. of 0.5 N sodium hydroxide used for 

neutralization ; 

m = molecular weight of the aldehyde or ketone; 
a = weight of sample in grams. 

Preparation of 0.5 N Hydroxylamine Hydrochloride Solution: 
Dissolve 275 g. of recrystallized hydroxylamine hydrochloride 96 
in 300 cc. of distilled water; warm to a temperature of 65 on a 
steam bath to yield a clear solution. Add this solution slowly 
to 2 gal. of 95% alcohol, and mix thoroughly. Then add 125 cc. 
of a 0.1% solution of bromphenol blue indicator in 50% alcohol, 
and sufficient 0.5 N alcoholic sodium hydroxide solution to 
change the yellow color of the solution to a greenish shade; 
this usually requires about 20 to 25 cc. of the alkali. The 
proper degree of neutralization is attained when 35 cc. of the 
solution shows a distinct greenish shade which changes to a dis- 
tinct yellow upon the addition of 1 drop of 0.5 N hydrochloric 
acid. A stable solution of hydroxylamine hydrochloride is thus 
obtained which is approximately 0.5 N ; an exact adjustment is 

For lesser quantities of solution, dissolve 34.75 g. of recrys- 
tallized hydroxylamine hydrochloride in 40 cc. of distilled water 
and make up to 1 liter with 95% alcohol; add 15 cc. of the 
bromphenol blue solution and neutralize. 

The proper size of sample and the proper length of time to give complete 
reaction and the molecular weights of the most frequently encountered alde- 
hydes and ketones are given in Table 4.12. 

Stillman-Reed Procedure: 97 Proceed as directed under the 
standard procedure but add 75 cc. of hydroxylamine solution, 
measured accurately by means of a burette or pipette. At the 
same time run a blank determination. After standing the re- 
quired length of time, titrate with standardized 0.5 N hydro- 
chloric acid to a green-yellow end point. Care should be taken 
to titrate both the blank and the sample to the same end point. 
Calculate the percentage of aldehyde or ketone as described 

96 In the case of very darkly colored oils, the size of sample should be greatly reduced and 
the end point determined with the aid of a spot plate. This is particularly important in the 
case of oils which have a greenish color e.g., wormwood oils. 

96 The hydroxylamine hydrochloride offered by Commercial Solvents Corp. under the 
name of "hydroxylammonium chloride" is sufficiently pure, after recrystallization from 
water, for the preparation of this solution. 

97 Perfumery Essential Oil Record 23 (1932), 278. 




Carbonyl Compound 

Molecular Wt. 

Size of Sample 

Reaction Time 

Acetaldehyde 44.05 

Acetophenonc 120.14 

a-Amyl Cinnamic Aldehyde 202.29 

Anisic Aldehyde 136.14 

Benzaldehyde 106.12 

Benzophenonef 182.21 

Benzylidene Acetone 146.18 

Butyraldehyde 72.10 

Camphorf 152.00 

Carvone 150.21 

Cinnamic Aldehyde . 132.15 

Citral 152.23 

CitroncllalJ 154.25 

Cuminic Aldehyde 148.20 

Decyl Aldehyde 156.26 

Dodecyl Aldehyde 184.31 

Ethyl Amyl Ketone 128.21 

Fenchonef 152.23 

Furfural 96.08 

Heliotropin 150.13 

Heptyl Aldehyde . ... 114.18 

Hexyl Aldehyde 100.16 

Hydrotropic Aldehyde. . 134.17 

lonone 192.29 

Irone 192.29 

Iso valeric Aldehyde 86.13 

Menthone 154.25 

Methyl Acetophenone 134.17 

Methyl Amyl Ketone 114.18 

Methyl Heptenone 126.19 

Methyl Heptyl Ketone 142.24 

Methyl Hexyl Ketone 128.21 











15 min. 
24 hr. 
15 min. 


15 min. 
15 min. 

24 hr. 
15 min. 
15 min. 
15 min. 
15 min. 

30 min. 
15 min. 

15 min. 

15 min. 

15 min. 
15 min. 
15 min. 
15 min. 

24 hr. 
1 hr. 
15 min. 

24 hr. 
15 min. 
15 min. 
24 hr. 
15 min. 
15 min. 

* All molecular weights have been calculated from the values of the International 
Atomic Weights adopted by the Committee on Atomic Weights in 1938. 

f Because of the slow reaction rate with hydroxylamine this method is not satisfactory 
for these ketones. 

t Low values are obtained for this isolate if the usual hydroxylamine hydrochloride 
technique is used. According to Dodge, fairly satisfactory results may be obtained if the 
solution is well cooled and the titration carried out at low temperatures (-10). Am. 
Perfumer, May (19*0), 43. 


TABLE 4.12 (Cord.}. 
PART I (Cont.) 

Carbonyl Compound 

Molecular Wt. 

Size of Sample 


Reaction Time 

VIethyl Nonyl Kctonc 
0-Methoxyacetophenone . . 



15 min. 
24 hr. 

Vonyl Aldehyde 
3ctyl Aldehyde 






15 min. 
15 min. 

15 min. 
30 min. 
15 min. 

15 min. 

Perillic Aldehyde. ... 

Phenylacet aldehyde 
Phenylpropyl Aldehyde 
Piperitonef . 
Salicyl Aldehyde . 

Thujone ... 
Tolyl Aldehyde .... 



24 hr. 
15 min. 

Undecyl Aldehyde 



15 min. 

Vanillin .... 
Valeric Aldehyde 



15 min. 
15 min. 


Mam Oarl>on>l Compound 


*"M7e of 




Sample (g ) 


Almond, Bitter 

Ben /aldehyde 




Caraway . . 

Carvone. ... 



24 hr. 


Cinnamic Aldehyde 



15 min. 

Cedar lxaf 




24 hr. 

Cherry Laurel . 






Cinnamic Aldehyde 



15 min. 

Citronella, Ceylon 




15 min. 

Citronella, Java. 




15 min. 


Cuminic Aldehyde 

1 18.20 


15 min. 





24 hr. 





24 hr. 


Decyl Aldehyde* 



30 min. 

* Occasionally the carbonyl component of grapefruit oil is imported as a mixture of equal 
parts of octyl and decyl aldehydes; if this is desired, use 142.24 as an average of the molecular 



TABLE 4.12 (Cord.). 
PART II (ConJ.) 

Main Carbonyl Compoum 

i Present 




Sample (g.) 






15 min. 

Lemon Concentrates, Ter- 
peneless and Sesquiter- 




15 min. 

Lernongrass. . . 




15 min. 

Limes, Distilled 




15 min. 

Limes, Expressed 




15 min. 

Mandarin . . 

Decyl Aldehyde 



30 min. 


Decyl Aldehyde 



30 min. 

Orange Concentrates, Ter- 
peneless and Sesquiter- 
peneless . 

Decyl Aldehyde 



30 min. 


I rone 



1 hr. 


Pulegone * 



about 72 hr. 





24 hr. 


Methyl Nonyl Ketone 



15 min. 

Sage, Dalmatian 




24 hr. 





24 hr. 





24 hr 

Wormwood 11 




24 hr 

t Very little citral is actually present in distilled lime oil. The carbonyl components 
consist mainly of octyl aldehyde, decyl aldehyde, dodecyl aldehyde, and an unidentified 
aldehyde. However, it is customary to report the aldehyde content as citral. 

J It is well to titrate the reaction mixture at the end of 1 hr. and then at the end of 24 hr : 
any appreciable difference in the two values indicates the presence of other carbonyl com- 
pounds, most likely one of the ionones. 

Because of the slow reaction rate of hydroxylamine with pulegone, this method is not 
satisfactory for oil pennyroyal ; use the neutral sulfite method. 

|| The dark color of wormwood oils with their natural greenish tint makes the determina- 
tion of thujone quite difficult. The use of a very small sample and the use of a spot-plate 
to judge the end point is recommended. However, the accuracy of the determination suffers 
thereby; nevertheless an accuracy of 5 per cent can be obtained. 


Preparation of 0.5 N Hydroxylamine Solution: Dissolve 20 g. 
of recrystallized hydroxylamine hydrochloride in 40 cc. of water 
and dilute to 400 cc. with 95% alcohol. To this solution, in a 
1 liter beaker, add, with stirring, 300 cc. of 0.5 N alcoholic 
potassium hydroxide and 2.5 cc. of a 0.4% bromphenoi blue 
solution in 50% alcohol. Permit the solution to stand for 30 
min. and filter. This solution cannot be stored for any appre- 
ciable period. A blank must always be run since the solution 
tends to deteriorate slowly. 

In conclusion it might be well to point out that each of the general 
methods for the determination of aldehydes and ketones has its place in the 
analysis of essential oils. Thus, absorption methods permit of the easy 
separation of the noncarbonyl portion of the oil and of the separation of 
some aldehydes and ketones by regeneration from the bisulfite addition 
compound with strong alkali. It then becomes possible to study the odor 
and other properties of these individual portions and to detect more readily 
adulteration of the original oil. A comparison of the results from the ab- 
sorption methods and from the hydroxylamine method is frequently very 
revealing; large differences may be indicative of adulteration with water- 
soluble constituents or additions of carbonyl compounds of low molecular 

From a consideration of the limitations of each method, it should be 
obvious that it is of utmost importance always to record the method used when 
reporting an analytical result. 


Phenols react with the alkali hydroxides, giving rise to water-soluble 
phenolates. This is the basis of the classical method 98 for the estimation of 
phenols in essential oils. Since the potassium salts of many phenols are 
more soluble than the corresponding sodium salts, the use of potassium 
hydroxide is preferred. 

It must be remembered that, in addition to the phenols, any alkali- 
soluble material (e.g., acids) will also go into solution as well as any water- 
soluble constituents or water-soluble adulterants (e.g., alcohol). This will 
give rise to erroneous results: the apparent phenol content will be too high. 
Further, an aqueous solution of alkali phenolates is a much better solvent 
for the nonphenolic portion of an oil than is the alkali solution itself; 
specifically this is important in the case of terpeneless bay oils. 

When the determination has been completed, it often proves of value to 
separate the nonphenolic portion and to study its odor. The alkaline solu- 
tion of the phenolates may be freed of traces of oil by washing with ether; 

98 The procedure was first applied by Gildemeister for the determination of phenols in 
thyme oil. 



the phenols may then be regenerated by the addition of dilute sulfuric acid 
(1:3), extracted with ether, and obtained in a pure state by evaporating off 
the ether. (The separated ether layer should be dried with anhydrous 
sodium sulfate before this final evaporation.) The presence of foreign 
phenolic bodies frequently may be detected by this technique. 

Modifications of the general procedure become necessary in the case of 
certain specific oils. Such modifications are noted below. 

General Procedure: Into a well cleaned 150 cc. cassia flask, 
having a long, thin neck graduated in 0.1 cc. divisions, introduce 
10 cc. of the oil, measured from a pipette. Add 75 cc. of an 
aqueous 1 N potassium hydroxide 
solution," measured from a gradu- 
ated cylinder. Stopper and shake 
thoroughly for exactly 5 min. Per- 
mit to stand undisturbed for 1 hr., 
after which the undissolved oil is 
forced into the neck by the addition 
of more potassium hydroxide solu- 
tion. The alkaline solution must be 
added carefully to avoid disturbing 
the layer of separated oil. (This 
addition may conveniently be made 
by clamping the flask at a slight 
angle on a ring stand; above the 
flask is placed a ring to hold a sepa- 
ratory funnel containing the solution 
of alkali which is permitted to flow 
down along the inside of the neck 
of the cassia flask very slowly. If 
the flow of the alkali is adjusted to 
about 1 drop per sec., a clean sepa- 
ration of the oil is usually obtained. 
(See Diagram 4.10.) In order to 
make any droplets of oil adhering to 
the sides of the flask rise into the 

neck, gently tap or revolve the flask rapidly between the palms 
of the hands. Measure the quantity of oil that does not dis- 
solve in the alkali. The phenol content, expressed as a vol- 
ume/volume percentage, is calculated from the following 
formula : 

Percentage of phenol = 10(10 no. of cc. of undissolved oil) 

99 Gildemeister and Hoffmann, "Die atherischen Ole," 3d Ed., Vol. I, 753, recommended 
the use of a 5 per cent solution of either NaOH or KOH be employed for thymol and car- 
vacrol-containing oils ; a 3 per cent solution for eugenol-containing oils. The official meth- 
ods of the "United States Pharmacopoeia" and the "National Formulary" require the use 
of KOH T.S. solution (1 N). 

DIAGRAM 4.10. Apparatus 
for Phenol determination. 


Oils containing large amounts of heavy metals may not give a sharp 
separation of the nonphenolic oily layer and the alkaline solution in the neck 
of the flask. Such oils should be thoroughly shaken with a small amount 
(about 1 per cent) of powdered tartaric acid and filtered to remove the 
interfering metals before the determination of phenols is attempted. 

Modification of the General Procedure: 

I. Clove Oils. Since clove oils contain aceteugenol in addi- 
tion to free eugenol and since both constituents contribute to 
the value of the oil it is customary to saponify the former and 
report the total phenol content as eugenol. The general pro- 
cedure is modified as follows : 

After thoroughly shaking the oil and alkali for 5 min. in the 
cold, heat the flask on a steam bath for 10 min. Occasionally 
shake the flask during this heating to insure complete saponifi- 
cation. Immediately after removal of the flask from the steam 
bath add a further quantity of alkali in order to drive the un- 
reacted oil into the neck of the flask. It is necessary to make 
this addition while the content of the flask is still hot since the 
nonphenolic portion may partially solidify. 

//. Pimento, Oils. The procedure described above for clove 
oils is also used for the determination of the phenol content of 
pimenta oils. 

///. Terpeneless Bay Oils. Because of the solvent effect 
of the potassium eugenolate upon the nonphenolic constituents 
of a terpeneless bay oil, the whole oil will go completely into solu- 
tion if a 1 N solution of potassium hydroxide is used in this 
determination. Therefore, it becomes necessary to reduce the 
strength of the alkali to 3% and to use 125 cc. of this dilute 
alkaline solution for shaking out the phenols. 

IV. Cinnamon OiJs. These oils offer some difficulty to the 
analyst. The formation of a troublesome emulsion and a very 
poor separation of the oil and the aqueous layers results because 
of the similarity of the gravity of the oil and the gravity of the 
solution. It is for this reason that a 3% solution cannot satis- 
factorily be used. Shaking for too long a period gives rise to 
results that are much too high. The following procedure, if 
followed exactly, will give results that can easily be duplicated, 
and which represent approximately the true eugenol content: 

To 50 cc. of a 1 N potassium hydroxide solution in a cassia 
flask add 5 cc. of the cinnamon oil. Shake well for exactly 3 
min. and let stand for 10 min. Fill the flask with potassium 
hydroxide solution, using the ring stand technique described 
under the general procedure. If the determination has been 
carried out carefully, the residual oil will rise into the neck in 
an unbroken column. 

V. Thyme and Origanum Oils. The phenolic constituents 
of thyme and origanum oils consists mainly of thymol and 
carvacrol. The separation of the phenolic constituents is an 


aid in the evaluation of these oils, since oils containing pre- 
dominently thymol are generally considered of superior quality. 
Thymol is easily crystallized ; carvacrol is a liquid at tempera- 
tures above 2. 

The separation and examination of the phenolic portion may 
conveniently be carried out after the determination of the phenol 

Pour the contents of the cassia flask (used in the assay) into 
a separatory funnel and permit the nonphenolic portion to 
separate. Filter the aqueous layer through filter paper pre- 
viously wetted with water. Transfer this filtered solution to a 
separatory funnel and acidify with dilute hydrochloric acid 
(1:3) until the mixture is strongly acid to litmus. Add 50 cc. 
of ether and shake thoroughly. Separate the ether layer, dry 
with anhydrous sodium sulfate and filter. Evaporate the ether 
cautiously on a steam bath and pour the liberated phenols into 
a test tube, and permit it to stand at room temperature for 30 
min. If the phenols consist primarily of thymol, a crystalline 
mass results. If no crystals form after 30 min., cool to 5 by 
means of an ice bath. Rub the side of the test tube with a 
thermometer or glass rod and add a small crystal of thymol to 
initiate crystallization: if no crystals form after 30 min. the 
absence of an appreciable amount of thymol may be assumed. 

In determining phenol contents it is well to remember that water- 
soluble constituents may be added to increase the apparent phenol contents. 
Alcohol and certain glycols are such adulterants which may be occasionally 
encountered. If the relationship between the specific gravity and the 
phenol content appears abnormal, the oil should be investigated further for 
the presence of possible adulterants. 


Of the numerous methods that have been proposed for the determination 
of the cineole content of essential oils, the method of Kleber and von 
Rechenberg, 100 the method of Cocking, 101 and that of Scammell 102 (modified 
by Baker and Smith 103 ) have proved the most valuable. 

According to the Kleber and von Rechenberg method, the congealing 
point of the oil itself is determined, from which the cineole content may be 
determined by reference to a table or graph. The presence of oxygenated 
constituents other than cineole has little effect upon the values obtained; 
an accuracy of about dbl per cent may be obtained. "The United States 
Pharmacopoeia" 104 makes use of this method to establish a minimum of 70 

100 /. prakt. Chem. [2] 101 (1920), 171. 

Analyst 52 (1927), 276. 

lo British Patent 14138 (1894). 

"Eucalypts and Their Essential Oils," 2nd Ed., Sydney, 1921, 364. 

104 Thirteenth Revision, 217. 



per cent cineole in official eucalyptus oils. The main criticism of the Kleber 
and von Rechenberg method is the inconvenience of working at greatly 
reduced temperatures. The exact determination of a congealing point at a 
temperature much below often presents difficulty. 

Procedure: Place about 10 cc. of the oil in a heavy walled 
tube which is preferably equipped with an air or vacuum jacket. 
Immerse the tube in a mixture of ice and salt, or in a cooling 
bath of solid carbon dioxide in acetone. The true solidification 
point is determined ; i.e., the temperature at which the crystals 
of cineole first appear as the oil is cooled, and at which the crys- 
tals disappear as the temperature is permitted to rise. Several 
determinations of the solidifying point should be made in order 
to obtain an exact reading. The percentage of cineole, corre- 
sponding to this temperature can be determined directly by 
reference to Table 4.13. 



Eucalyptol Content 



Eucalvptol Content 

' (%) 



- 9.0 










































The o-cresol method of Cocking offers certain advantages. Since the 
congealing point is well above room temperature, the determination is 
greatly simplified. Results are easily reproducible. According to Cocking, 
the accuracy is approximately 3 per cent in the case of eucalyptus and 
cajuput oils. The o-cresol method has been accepted as the official method 
of "The British Pharmacopoeia." 106 The procedure as given below is 
essentially the official method of "The British Pharmacopoeia." 

Procedure: Into a stout walled test tube, about 15 mm. in 
diameter and 80 mm. in length, place 3 g. (accurately weighed) 
of the oil, previously dried with anhydrous sodium sulfate, 106 

'< (1932), 584. 

10 * The use of calcium chloride for drying the oil as suggested by "The British Pharma- 
copoeia" is not to be recommended ; anhydrous sodium sulfate is much to be preferred, 
eliminating the possibility of formation of addition products with primary alcohols that 
may be present in the oil. 


together with 2.1 g. of melted o-cresol. The o-cresol used must 
be pure and dry, with a freezing point not below 30. It is 
hygroscopic and should be stored in a small well-stoppered 
bottle, because the presence of moisture may lower the results. 
Insert a thermometer, graduated in fifths of a degree, and 
stir the mixture well in order to induce crystallization ; note the 
highest reading of the thermometer. Warm the tube gently 
until the contents are thoroughly melted, and insert the tube 
through a bored cork into a widemouthed bottle which is to act 
as an air jacket. The thermometer should be suspended from a 
ring stand in such a way that it does not touch the walls of the 
inner tube. Allow the mixture to cool slowly until crystalliza- 
tion commences, or until the temperature has fallen to the point 
previously noted. Stir the contents of the tube vigorously with 
the thermometer, rubbing the latter on the sides of the tube 
with an up and down motion in order to induce rapid crystal- 
lization. Continue the stirring and rubbing as long as the tem- 
perature rises. Take the highest point as the freezing point. 
Repeat this procedure until two readings agreeing within 0.1 
are obtained. The percentage of cineole in the oil can be com- 
puted from Table 4.14. 

It should be noted that in both methods relatively high cineole contents 
give more accurate analytical results. Therefore, if the cineole content of 
the oil is low, the determination is best carried out on a mixture of equal 
parts (by weight) of oil and pure cineole, (melting point, 1.2 or higher). 
In the Kleber and von Rechenberg method, if the cineole content is less than 
65 per cent, this modified procedure should be followed; in the o-cresol 
method, of Cocking, if less than 50 per cent. The cineole content of the 
original oil may then be calculated by means of the following formula : 

Percentage of cineole in original oil = 2 X (% of cineole in mixture 50) 

The phosphoric acid method of Scammell as modified by Baker and 
Smith is based on the formation of a solid, loose molecular compound of 
cineole and phosphoric acid from which the cineole may be regenerated by 
the addition of water. The procedure recommended by these authors is 
given below : 

Procedure: Place 10 cc. of the oil in a 50 cc. beaker or other 
suitable vessel and cool thoroughly in a bath of ice and salt. 
Slowly add 4 cc. of phosphoric acid, 107 a few drops at a time, 
mixing the acid and oil thoroughly between each addition by 
careful stirring. After all of the acid has been added, permit 
the mixture to remain in the bath for 5 min. to insure complete 
formation of the cineole-phosphoric acid addition compound. 
Then add 10 cc. of petroleum ether (boiling below 50) which 

107 If the cineole content is below 30 per cent, add only 3 cc. of phosphoric acid. 














































































































































has previously been well cooled in the ice bath and incorporate 
well with the aid of a flat ended rod. Immediately transfer the 
mixture to a cooled Buchner funnel, 5 cm. in diameter. Filter 
off the noncombined portion rapidly with the aid of a water 
pump. Transfer the cake from the Buchner funnel to a piece 
of fine calico and spread the cake with a spatula so that it covers 
an area of about 6 X 8 cm. Fold over the calico into a pad and 


place between several layers of absorbent paper. Press well for 
3 min. Break up the cake on a glazed tile with a spatula and 
transfer to a cassia flask. Decompose the cineole-phosphoric 
acid addition compound with warm water and force the liber- 
ated cineole into the neck of the flask by the further addition of 
water. After the separation is complete and the contents of 
the flask have cooled to room temperature measure the amount 
of cineole. 

If the cineole content is found to be above 60 per cent, repeat the de- 
termination using a sample of the oil diluted with freshly distilled pinene 
or turpentine oil : three volumes of oil plus one volume of pinene. Make the 
necessary correction in calculating the percentage of cineole. 

This test gives satisfactory results with oils containing as little as 20 
per cent cineole and as high as 100 per cent; in the latter case, the oil must 
be previously diluted as described. It is important to add the acid slowly, 
to have the mixture very cold and to cool the petroleum ether thoroughly 
before adding. 

Other methods for the quantitative determination of cineole have been 
suggested. In their monumental work on the eucalypts Baker and Smith 108 
give a brief criticism of many of these methods. 


The analysis of wormseed oils offers some difficulty because of the lack 
of a satisfactory method for the determination of the active principle, 

"The United States Pharmacopoeia" 109 based the official determination 
on the fact that ascaridole is soluble in dilute acetic acid. The technique 
consists of shaking a measured volume of the oil in a cassia flask with 60 
per cent acetic acid, determining the volume of undissolved oil, and calcu- 
lating the ascaridole content by difference. This is a method developed by 
Nelson. 110 Although this procedure represents one of the simplest determi- 
nations for ascaridole, it suffers from the fact that the analytical values are 
far from accurate. It has been found that normal oils containing as much 
as 70 to 80 per cent ascaridole (as indicated by solubility, gravity, distilla- 
tion, and other methods for the determination of ascaridole) often analyze 
as low as 55 per cent by the Nelson method. Furthermore, Reindollar 111 
has shown that "hi-test" oils containing large amounts of ascaridole give 
results by this method that are too high. A further disadvantage of the 
Nelson method lies in the fact that the determination is by no means specific 

" "The Eucalypts," 2nd Ed. (1920), Sydney, Australia, p. 357. 

Eleventh Revision, 251. 

"/. Am. Pharm. Assocn. 10 (1921), 836. 

m Ibid. 28 (1939), 591, 


for ascaridole; additions of cineole or cineole-containing oils analyze as 
ascaridole. This is also true of many other oxygenated compounds, such as 

Procedure: Place 10 cc. of oil wormseed, measured from a 
pipette, in a 100 cc. cassia flask. Add 50 cc. of a solution of 
acetic acid made by diluting 60 cc. of glacial acetic acid with 
distilled water to measure 100 cc. Shake the mixture well for 
5 min. Add sufficient of the acetic acid solution to raise the 
lower limit of the oily layer within the graduated portion of the 
neck and allow the liquids to separate, rotating the flask from 
time to time. Note the volume of the oily layer. 

Percentage of ascaridole = 10(10 cc. of unreacted oil) 

In order to overcome these difficulties, "The United States Pharma- 
copoeia" 112 later abandoned the Nelson method and then substituted the 
Cocking and Hymas 113 procedure, previously official in "The British Pharma- 
copoeia." 114 The procedure given below is based upon this official method: 

Assay: Place about 2.5 g. of oil chenopodium, accurately 
weighed, in a 50 cc. volumetric flask, fill to the mark with 90% 
acetic acid, mix well, and transfer a portion of this freshly pre- 
pared solution to a burette, graduated in 20ths of a cc. Into 
a glass-stoppered Krlenmeyer flask measure, from graduated 
cylinders, 3 cc. of a solution of potassium iodide (prepared by 
dissolving 8.3 g. of potassium iodide in sufficient distilled water 
to make 10 cc. of solution), 5 cc. of concentrated hydrochloric 
acid, and 10 cc. of glacial acetic acid. Immerse the flask in a 
freezing mixture until the temperature is reduced to 3, add 
quickly about 5 cc. of the acetic acid solution of the oil, mix it 
with the cooled reagent as rapidly as possible, and observe the 
volume drawn from the burette after 2 min. (to allow for drain- 
ing). Set the stoppered flask aside at a temperature between 
5 and 10 for exactly 5 min. ; then, without diluting, titrate the 
liberated iodine with tenth-normal sodium thiosulfate. At the 
same time, conduct a blank test, but dilute the reagent with 20 
cc. of distilled water before titrating the liberated iodine. The 
difference between the two titrations represents the iodine 
liberated by ascaridole. Each cc. of tenth-normal sodium 
thiosulfate is equivalent to 0.00665 g. of CioHi 6 2 . 116 

If all conditions as outlined are rigidly followed, this method gives an- 
alytical results that are reproducible and relatively accurate for normal 

112 Twelfth Revision, 319. (Now official in "The National Formulary," Eighth Ed., 136.) 

"' Analysts* (1930), 180. 

" (1932), 303. 

116 Pauly (sec Pharm. Arch. 7 (1936), 9) contends that the empirical factor, 0.00665, is 
actually too high, since he obtained a value of 110 per cent for a redistilled ascaridole frac- 
tion using this factor. Experiments carried out in the laboratories of Fritzsche Brothers, 
Inc., appear to confirm this fact. 


American oils. If, however, the ascaridole content is abnormally low, 
the results will not be sufficiently accurate. 

Since this method is based on the oxidation of potassium iodide by the 
peroxide, ascaridole, and the subsequent determination of the amount of 
free iodine, additions of oxygenated constituents should not increase the 
apparent ascaridole content unless the added compound is capable of 
oxidizing the potassium iodide under the experimental conditions. Further- 
more, since the liberated iodine is capable of being absorbed by unsaturates 
in the oil, it is very important to maintain the low temperatures as indicated 
in the procedure, to keep this secondary reaction at a minimum. 

The tentative method for the determination of ascaridole as outlined in 
the Methods of Analysis of the Association of Official Agricultural Chem- 
ists 116 proves too cumbersome for rapid commercial analyses and control. 
This method, developed by Paget, 117 involves the reduction of ascaridole by 
titanium trichloride. It requires that the solution be protected from at- 
mospheric oxygen ; this entails storage of the solution under an atmosphere 
of hydrogen, and titrations under an atmosphere of carbon dioxide. Ac- 
cording to the experiments of Reindollar, 118 the results obtained by this 
method are fairly concordant with those obtained by the method of Cocking 
and Hymas. The Association of Official Agricultural Chemists' method is 
given below, exactly as it appears in this official work : 

Procedure: " Weigh 1 mi of the oil in 100 ml volumetric flask 
and dilute to volume with alcohol. Place 50 ml of the TiCl 3 
soln in Erlenmeyer flask through which current of CO-2 is pass- 
ing. Fit flask uith Bunsen valve, add 10 ml of diluted soln of 
the oil, close flask (with the Bunsen valve), and heat contents 
almost to boiling for 2 min. (Prolonged heating has no effect 
if contents are not boiled vigorously.) If pale violet color of 
the TiCU disappears, add more reagent to insure excess. (For- 
mation of a white precipitate does not interfere with determina- 
tion.) Add 1 ml of 5% NH 4 CNS soln and titrate back excess 
of TiCU with the FeNH 4 (S0 4 ) 2 soln in CO 2 atmosphere until 
faint, permanent, brownish red color is obtained. 

"Subtract quantity of FeNH 4 (S0 4 ) 2 soln used, expressed in 
equivalent mg of TiCl 3 , from number of mg of TiCU taken. 
Difference is number of mg of TiCU oxidized by oil taken. Con- 
vert mg of TiCU oxidized into ascaridole by dividing by factor 
1.284 (1 g of ascaridole is reduced by 1.284 g of TiCl 3 ). 

"Example : 0.9600 g of oil was made up to 100 ml and 10 ml 
aliquot was heated with 50 ml of the TiCl 3 soln (1 ml containing 
0.0034 g of TiCU). It then required 5.9 ml of the reagent, each 
ml equivalent to 0.01545 g to TiCU, to back titrate. Grams of 

" 6th Ed., 735. 

AnalystSI (1926), 170. 

118 /. Am. Pharm. Assocn. 28 (1939), 589. 


TiCl 3 oxidized is numerically equal to (50 X 0.0034) - (5.9 
X 0.01545), or 0.07885. Weight of oil in the aliquot was 

0.0960 g. Hence percentage of ascaridole = ' TOO~ 

0.096 X 1.284 
= 72.1%. 

"a) Standard ferric ammonium sulfate soln. Dissolve 
39.214 g of pure, crystallized Fe(NH 4 )2(SO 4 )2-6H 2 in 200 ml 
of H 2 in liter flask, add 30 ml of H 2 SO 4 , and mix well. Weigh 
exactly 3.16 g of KMnO 4 , dissolve in 200 ml of warm H 2 O, and 
slowly add to soln in the flask, with stirring. (KMn0 4 soln 
should be just sufficient to oxidize the ferrous salt, but it is well 
to add the last few ml in small portions.) Cool soln and dilute 
to 1 liter with H 2 0. 

"b) Standard titanium trichloride soln. Add 100 ml of com- 
mercial 15-20% TiCl 3 soln to 200 ml of HC1, boil 1 min., cool, 
and dilute to 4500 ml with H 2 0. Place soln in container with 
II atmosphere provision and allow to stand 2 days for absorp- 
tion of residual 0. Preserve the TiCla soln in an atmosphere of 
H (Chap. 21, Fig. 27), taking care to have all joints air-tight, 
and covering stoppers (preferably countersunk) with suitable 
wax. Standardize by titrating 20 ml of the FeNH 4 (S0 4 ) 2 soln 
against the TiCls soln in a protective stream of C0 2 , using 1 ml 
of 5% NH 4 CNS soln as indicator. 1 ml of 0.1 .V FeNII 4 (SO 4 ) 2 
= 0.01545 g of TiCl 3 ." 

The determination of the ascaridole content by a distillation technique 
is not to be recommended for routine analyses, since the ascaridole is so 
unstable that the oil is apt to decompose with explosive violence should the 
temperature not be carefully controlled. 

Dodge 119 has suggested the use of a solution of sodium bisulfite to de- 
termine the ascaridole content of wormseed oils. The difficulty of determin- 
ing the exact end point and the length of time required for a determination 
militates against the use of this technique. 

In spite of its recognized deficiencies, the method of Cocking and Hymas, 
at the present time official in "The National Formulary," Eighth Ed., and 
"The British Pharmacopoeia," is probably the most useful for commercial 
analytical control laboratories. 


In order to determine the camphor content of essential oils (which con- 
tain no other carbonyl compounds) the gravimetric determination proposed 
by Aschan 120 may be employed. 

Procedure: Introduce about 1 g. of the oil, accurately 
weighed, into a test tube and dissolve the oil in 2 g. of glacial 

119 Drug & Cosmetic Ind. 46 (1940), 414. 

120 Finska Apoth. Tidskrift (1925), 49. Chem. Abstracts 20 (1926), 1775. 


acetic acid. Add 1 g. of semicarbazide hydrochloride and 1.5 g. 
of freshly fused anhydrous potassium acetate. Triturate 
thoroughly with a glass rod, stopper the tube with a plug of 
absorbent cotton and heat three hours in a water bath at 70. 
Cool the mixture, add 10 to 15 cc. of water, stir thoroughly and 
transfer the precipitate quantitatively to a tared 4 to 5 cm. 
filter. Wash with water until all water soluble matter is re- 
moved, air dry, wash with petroleum ether and dry in air to 
constant weight. Determine the weight of semicarbazone from 
the increase in the weight of the filter. Calculate the content 
of camphor in the original oil by means of the following formula : 

fff\ > *f~. 
Percentage of camphor = ' 


where : p weight of semicarbazone in grams ; 
8 = weight of oil in grams. 


The procedure described below is based on the classical method of Hesse 
and Zeitschel. 121 It depends on the actual separation of the ester from the 
volatile oil by the formation of the ether insoluble sulfate. 

Procedure: Dissolve about 25 to 100 g. of oil in twice the 
volume of anhydrous ether. Cool the solution well in a freezing 
mixture, the temperature being reduced to at least 0. Add, 
with constant stirring, a solution of 1 volume of concentrated 
sulfuric acid in 5 volumes of anhydrous ether until no further 
precipitate forms. Collect the precipitate in a small, well- 
cooled Buchner funnel and wash with dry, cold ether until 
odorless. Dissolve this precipitate in water with the aid of 
alcohol if necessary, and titrate with 0.5 N sodium hydroxide. 
Calculate the ester content by means of the following formula : 

Percentage of methyl anthranilate = 


where: a = cc. of alkali required; 

s original weight of oil taken in grams. 

To this solution add an excess of 0.5 N sodium hydroxide and 
heat the mixture on a steam bath for 30 min. Titrate the free 
alkali which is unconsumed with 0.5 N hydrochloric acid. Cal- 
culate again the ester content by means of the following formula : 

fj C CL 

Percentage of methyl anthranilate = - : 


where : b = cc. of alkali consumed in the saponification ; 
s original weight of oil taken in grams. 

"Bar. 34 (1901), 296. 


If the ester is exclusively methyl anthranilate, a should be twice 
as large as 6. 

The procedure as described will determine all basic constituents which 
form ether insoluble sulfates (e.g., the methyl ester of methyl anthranilic 
acid) in addition to methyl anthranilate. 

For the determination of methyl anthranilate in the presence of methyl 
N-methyl anthranilate, Erdmann 122 has suggested a procedure based on the 
diazotization of methyl anthranilate, a primary aromatic amine. The ester 
is washed out of the oil with dilute sulfuric or hydrochloric acid, and the 
acid solution treated with a 5 per cent sodium nitrite solution to diazotize 
the amine. The solution is then titrated with an alkaline solution of /3-naph- 
thol. (This solution is prepared by dissolving 0.5 g. /3-naphthol in 0.5 cc. 
of sodium hydroxide, at least 30 per cent, and adding a solution of 15 g. of 
sodium carbonate in 150 cc. of water.) The azo dye thereby formed is 
insoluble and precipitates out. The titration is continued until no further 
precipitation occurs. 

A combination of the method of Hesse and Zeitschel and that of Erdmann 
can be used to determine the percentage of methyl anthranilate and of 
methyl N-methyl anthranilate. 


Several methods, both volumetric and gravimetric, for the determination 
of allyl isothiocyanate in mustard oils have been suggested in the litera- 
ture. 123 The most satisfactory one is a modification of the official procedure 
of "The United States Pharmacopoeia/' 124 This method is based upon the 
reaction of the isothiocyanate radical with silver nitrate. The excess silver 
nitrate solution is determined by titration with standardized ammonium 
thiocyanate solution in the presence of ferric ion ; the titration must be con- 
tinued until the red color of ferric thiocyanate is first observed. 

C 3 H 6 NCS + NH 4 OH + AgNO 3 - AgNCS + C 3 H 6 OH + NH 4 NO 3 

Procedure: Dilute about 4 cc. of the oil, accurately weighed, 
with sufficient alcohol to make exactly 100 cc. of solution. 
Pipette 5 cc. of this solution into a 100 cc. mustard oil flask (see 
Diagram 4.11) and add 50 cc. of 0.1 N silver nitrate solution 
and 5 cc. of 10% ammonia solution. Connect the flask to an 
air-cooled reflux condenser, 1 m. long, and heat on a steam 
bath for 1 hr. Allow the liquid to cool to room temperature 
and then add sufficient distilled water to fill the flask to the 100 
cc. mark. Mix well and filter through a dry filter. Reject 

i"Ber. 35(1902), 24. 

See "Suggested Additional Literature," p. 359. 

124 Twelfth Revision, 46. (Now official in "The National Formulary," Eighth Ed., 29.) 



the first 10 cc. of filtrate. Transfer 50 cc. of the subsequent 
filtrate by means of a pipette into a 100 cc. saponification flask; 
add about 5 cc. of concentrated nitric acid 
and 2 cc. of an 8% solution of ferric am- 
monium sulfate. Titrate the excess of sil- 
ver nitrate solution with standardized 0.1 
N ammonium thiocyanate. Carry out a 
blank determination simultaneously, using 
5 cc. of alcohol and the same quantities of 
reagents but omitting the oil. Calculate 
the percentage of allyl isothiocyanate; each 
cc. of 0.1 N silver nitrate is equivalent to 
0.004958 g. of allyl isothiocyanate. 

Percentage of allyl isothiocyanate 

19.832 (b - a) 

where: b = cc. of ammonium thiocyanate 
solution required for the blank; 
a = cc. of ammonium thiocyanate 
solution required for the deter- 
11 ^ mination ; 

DIAGRAM 4.11. w = weight of oil used for the original 

Mustard oil flask. dilution. 

The blank should require about 24 to 25 cc. of ammonium thiocyanate; 
the actual determination, about 4 to 5 cc. if a 4 g. sample of oil is employed. 


Hydrogen cyanide occurs in the distillates of a number of plants. It 
plays an important part in the medicinal value of oil of bitter almond and 
oil of cherry laurel. The presence of hydrogen cyanide can be ascertained 
qualitatively by means of the Prussian blue test. 

Procedure: To 1 cc. of the oil in a test tube add 1 cc. of dis- 
tilled water, a few drops of a 10% aqueous sodium hydroxide 
solution and a few drops of a 10% ferrous sulfate solution. 125 
Shake thoroughly and acidify with dilute hydrochloric acid. 
The precipitate of ferrous and ferric hydroxides dissolves, and 
in the presence of hydrogen cyanide the characteristic precipi- 
tate of Prussian blue appears. 

In order to determine quantitatively the amount of hydrogen cyanide 
in an oil the titrimetric method of "The United States Pharmacopoeia" 126 

125 Such a solution of ferrous sulfate always contains a small amount of ferric salt which 
is necessary for this reaction. 

1M Twelfth Revision, 314. (Now official in "The National Formulary," Eighth Ed., 31 .) 


has proved satisfactory. This method is based upon precipitation of the 
cyanide by silver nitrate solution.. The end point of the reaction can be 
determined by the red color of silver chromate. Part of the hydrogen 
cyanide found in oil of bitter almond and oil of cherry laurel is bound with 
benzaldehyde in the form of cyanhydrin ; in order to liberate this hydrogen 
cyanide, a small amount of freshly precipitated magnesium hydroxide is 

Procedure: Dissolve 0.75 g. of magnesium sulfate in 45 cc. of 
distilled water. Add 5 cc. of 0.5 X sodium hydroxide solution 
and 2 drops of a 10% solution of potassium chromate, and titrate 
the solution with 0.1 N silver nitrate solution to the production 
of a permanent reddish tint; this requires but a few drops of the 
silver nitrate solution. Pour this mixture into a 100 cr . Erlen- 
meyer flask containing 0.5 g. of oil of bitter almond accurately 
weighed. Mix well and titrate again with 0.1 N silver nitrate 
solution until a red tint, which does not disappear upon shaking, 
is produced. Conduct this titration as rapidly as possible. 
Calculate the hydrogen cyanide content by means of the follow- 
ing formula : 

*i i -i 0.2702a 

Percentage of hydrogen cyanide = 


where: a = number of cc. of 0.1 N silver nitrate required; 
s = \veight of sample in grams. 


The iodine number of a fat or oil represents the number of grams of 
iodine capable of being absorbed under certain fixed conditions by 100 g. 
of the substance. It is an indication of the degree of unsaturation in the 
fatty acid radical of the glycerides. 

The use of iodine numbers for the evaluation of essential oils has never 
attained practical significance. This is due primarily to the unpredictable 
behavior of such oils in the presence of iodine solutions. It has been shown 
frequently that the iodine numbers of many essential oils vary with the size 
of the sample as well as with the period of contact with the reagent. Fur- 
thermore, the results do not correspond with the theoretical values expected. 

In the case of fixed oils the iodine number is an important criterion of 
purity. Since the essential oil chemist occasionally is faced with the 
evaluation of such fixed oils as persic oil, sweet almond oil, olive oil, castor 
oil, and sesame oil, a procedure for the determination of iodine numbers is 
included here. 


Procedure: 1 * 7 Introduce about 0.25 g. of the oil, accurately 
weighed, 128 into a glass stoppered Erlenmeyer flask of 250 cc. 
capacity, dissolve it in 10 cc. of chloroform, add 25 cc. of iodo- 
bromide solution, accurately measured from a burette, stopper 
the vessel securely, and allow it to stand for 30 min. 129 pro- 
tected from light. Then add in the order named 30 cc. of a 
1 N potassium iodide solution and 100 cc. of distilled water, 
and titrate the liberated iodine with tenth-normal sodium thio- 
sulfate, shaking thoroughly after each addition of thiosulfate. 
When the iodine color becomes quite pale, add 1 cc. of a 1% 
starch indicator solution and continue the titration with thio- 
sulfate until the blue color is discharged. Carry out a blank 
test at the same time with the same quantities of chloroform and 
iodobromide solution, allowing it to stand for the same length 
of time and titrating as directed. The difference between the 
number of cc. of thiosulfate consumed by the blank test and the 
actual test, multiplied by 1.269 and divided by the weight of 
sample taken, gives the iodine number. If more than half of 
the iodobromide solution is absorbed by the sample of the sub- 
stance taken, the determination must be repeated, using a 
smaller sample of the substance under examination. 

The iodobromide solution may be prepared by the following method : 

Dissolve 13.2 g. of reagent iodine in 1,000 cc. of glacial 
acetic acid with the aid of gentle heat if necessary. Cool the 
solution to 25 and determine the iodine content in 20 cc. by 
titration with tenth-normal sodium thiosulfate. Add to the 
remainder of the solution a quantity of bromine equivalent to 
that of the iodine present. Preserve in glass-stoppered bottles, 
protected from light. 



A study of the odor and flavor of an oil, isolate, or synthetic is essential 
in judging quality and aids in the detection of adulteration. Comparison 
should always be made with an oil of good quality and of known purity. 
Organoleptic tests are unquestionably the most sensitive and satisfactory 
method for detecting slight spoilage in oils such as the citrus oils, and in 

m The procedure given is essentially the official method of "The United States Pharma- 
copoeia," Thirteenth Revision, 647 (Hanus Method). 

128 The weight of the oil used is best determined by weighing by difference. A small 
bottle containing a few cc. of the oil and also a medicine dropper is accurately weighed ; 
then about 8 or 9 drops of the oil are introduced into the Erlenmeyer flask, and the bottle 
with the residual oil and medicine dropper is again accurately weighed: the difference 
represents the weight of sample used.*. Small "petit cups" of glass may also be used ; these 
cups (containing the requisite amount of oil, accurately weighed) are dropped into the 
Erlenmeyer flasks and' ate not removed during the determination. 

U9 In the case of castor oil, allow the mixture to stand for 60 min. 


detecting burned, pyroligneous "by-notes" resulting from improper dis- 

Procedure Water Flavor Test: Place J oz. of alcohol in an 
8 oz. glass. Add 1 drop of oil and then 7 oz. of cold water, the 
water being added slowly with vigorous stirring. This should 
yield a clear or opalescent mixture, which does not separate 
oily droplets on the surface. The odor and flavor of these two 
water flavor tests should be carefully studied and evaluated. 

In the case of dill oils, it is well to add 3 drops of glacial acetic acid to 
approximate more accurately the conditions under which this oil is usually 
employed. In the case of peppermint oils, it is best to add hot water; 
the flavor tests should be of uniform temperature and tasted while still 

Procedure Sugar Syrup Test: An acidified sugar syrup is 
prepared by adding 1 dram of 85% syrupy phosphoric acid and 
7 drams of 50% citric acid to 1 gal. of simple syrup (U.S. P. 
quality: approximately 65% wt./wt.). Dilute 2 oz. of this 
prepared syrup with 2 oz. of cold water. Add 1 to 3 drops of a 
10% alcoholic solution of the oil and mix thoroughly. The 
odor and flavor of these two sugar syrup tests should be carefully 
studied and evaluated. 

These syrup tests are best prepared in widemouthed, screw-top bottles 
which permit of thorough mixing of the alcoholic solution and the syrup 
by vigorous shaking. 

Such syrup flavor tests are especially valuable in evaluating citrus oils 
citrus concentrates, and oils and synthetics which duplicate the flavor o1 
highly acidic fruits. 

In the case of sweetening agents (such as vanillin, coumarin, and helio- 
tropin), it is well to dispense with the acidic medium and to use instead * 
mixture of equal parts of simple syrup and water. 

It should be remembered that comparison with a product of good quality 
is essential. 


The presence of chlorine in a synthetic is usually indicative of insufficien 
purification. The detection of halogen in a reputedly natural essentia 
oil or fraction is indicative of adulteration with a chlorine-containing syn 
the tic. For example, cassia oils showing the presence of chlorine hav< 
probably been adulterated with impure synthetic cinnamic aldehyde. 

Of the numerous procedures which hve been suggested, the classica 
test with copper oxide (the so-called Beilstein test) groves by far the mos 
convenient and rapid. Should this test prove inconclusive, the presence o 


absence of halogen should be confirmed by the combustion method, a more 
sensitive test. 

Procedure /. Beilstein Method: Wind the end of a No. 16 
gage 130 copper wire into a tight spiral about 6 mm. long and 6 
mm. in diameter. Fasten the other end of this wire to a wooden 
handle. Heat the wire in the nonluminous flame of a Bunsen 
burner until it glows without coloring the flame green. 131 Per- 
mit the wire to cool and reheat several times until a good coat 
of oxide has formed on the coil. 132 Add to the cooled spiral 2 
drops of the material to be tested. Ignite and permit it to burn 
freely in air. The wire is again cooled and 2 more drops of the 
material are added and burned. This process is continued until 
a total of 6 drops has been added and ignited. Then hold the 
spiral in the oxidizing portion of a Bunsen flame, adjusted to 
about 1 in. high. If the material is free from halogen, the 
flame will show no green color. The degree of persistence of 
green color is a rough indication of the amount of halogen pres- 
ent. A highly purified synthetic, free from halogen, will not 
show even a transient green color or flash of green. 

Instead of the wire spiral described above, a piece of 30 mesh copper 
screening (1.5 cm. X 5.0 cm.) may be used. The screening should be rolled 
tightly around a copper wire and held in position by bending back the wire 
and twisting securely. Such a roll of copper screening will hold about 1 cc. 
of oil because of surface tension. 

Certain nitrogen-containing compounds may give a positive test al- 
though no halogen is present. Also, the presence of free organic acids may 
cause a green colored flame since the copper salt may be sufficiently volatile ; 
e.g., phenylacetic acid. Therefore, if a positive test is obtained, it is best 
to confirm such findings by the combustion method. 

Procedure //. Combustion Method: 1 A piece of filter paper 
about 5X6 cm. is folded and saturated with the oil to be tested. 
The paper is placed in a small porcelain evaporating dish which 
rests in a larger watch glass. The paper is ignited and covered 
immediately with a 2 liter beaker, the inner surface of which has 
been previously moistened with water. (The watch glass should 
be sufficiently large to extend beyond the rim of the beaker.) 
After the flame has died out, the beaker is permitted to remain 
in position for 5 min. The porcelain evaporating dish is re- 
moved, and the products of combustion, which have condensed 
on the inner surface of the beaker, are washed into the watch 

130 A No. 16 gage wire has a diameter of 0.065 in. 

131 Too intense a heat is to be avoided since the copper spiral will then fuse and will 
offer less surface in the subsequent test. 

132 These wires may be used repeatedly. After many determinations, the wire becomes 
somewhat porous and well coaied with oxide. Such wires prove very satisfactory. 

183 Mr. Schimmel & Co. April (1890), 29; October (1904), 57. 


glass with about 10 cc. of distilled water and then poured into a 
filter. 134 Add to the filtrate 1 drop of nitric acid and 1 cc. of 
0.1 N silver nitrate solution. If the oil is free from halogen, no 
turbidity should result. Since this method will detect even 
minute traces of chlorine, it is absolutely necessary to run a 
blank. 135 

Several other tests have been described, such as the lime test, 136 the test 
employing sodium peroxide, 137 and the classical test employing molten 
metallic sodium. 138 The last named test is perhaps the most sensitive, but 
it suffers from the inherent disadvantages of working with metallic sodium. 

A special test for the detection of side chain chlorine in cinnamic alde- 
hyde has been accepted as official in the "National Formulary/' Eighth 
Edition, Monograph on cinnamic aldehyde. It indicates the presence of 
chlorine only when it appears in the side chain. This is not intended as a 
general test for the detection of side chain halogen in all compounds. How- 
ever, it has proven satisfactory for such synthetics as cinnamic aldehyde. 

Procedure: 1 To a 1 cc. sample of cinnamic aldehyde add 
10 cc. of commercial isopropanol, 1 cc. of nitric acid (1:1) and 
1 cc. of 1 0% silver nitrate solution. Shake the mixture after the 
addition of each reagent. Heat to incipient boiling and permit 
the test tube to stand for 5 min. If chlorine is present in the side 
chain, opalesconce or turbidity will result. Carry out simul- 
taneously a blank in order to assure absence of chlorine in the 

When recording the presence of halogen always designate the method 
employed. Also, an estimate of the relative amount of halogen present 
should be given; use may be made of such relative phrases as "strongly 
positive," "moderately positive," "slightly positive," "positive -.traces/' 
and "negative." 


Heavy metals are often present as impurities in essential oils. It is 
especially important that oils be free from such impurities if they are to be 
used for medicinal purposes or in foodstuffs. Furthermore, the presence of 

134 The filter is best prepared by thoroughly washing a small filter paper in a glass funnel 
with distilled water until the water passing through fails to show any turbidity or opalescence 
when treated with a drop of nitric acid and 1 cc. of the silver nitrate solution. 

136 Some filter papers contain sufficient amounts of chlorine to give a positive test. 

136 Gildemeister and Hoffmann, "Die atherischen Ole," 3d Ed., Vol. I, 779. 

137 "The United States Pharmacopoeia," Thirteenth Revision, 104. 

138 Directions for the ignition with metallic sodium have been admirably described by 
Mulliken in his classical work, "A Method for the Identification of Pure Organic Com- 
pounds," John Wiley & Sons, Inc., New York Vol. I (1904), 10. 

139 "The National Formulary," Eighth Edition, 153. 


heavy metals in perfume oils will often cause discoloration in such products 

as soaps and cosmetic creams. 

A very sensitive test for heavy metals has long been official in "The 

United States Pharmacopoeia" 140 to insure the absence of lead and copper. 

The test is based upon the fact that hydrogen sulfide will react with the 

chlorides of these metals to give dark colored sulfides. 

The sulfides of most metals are black or brownish black. The following 

represent the exceptions : the sulfides of cadmium, arsenic and tin (stannic 

form) are yellow; of antimony, orange; and of zinc, white. This test is 

especially satisfactory for the determination of small amounts of copper or 


Procedure: Shake 10 cc. of the oil with an equal volume of 
distilled water to which 1 drop of concentrated hydrochloric 
acid has been added, and pass hydrogen sulfide through the 
mixture until it is saturated. No darkening in color in either 
the oil or the water is produced in the absence of heavy metals. 
In order to discern any darkening if only traces of heavy metals 
are present, it is necessary to carry out simultaneously a blank 
determination to which no hydrogen sulfide is added: a com- 
parison of the blank and the run will clearly indicate traces of 
heavy metals if present. Test tubes may be conveniently used 
for these determinations. 

Often a scum will form at the surface between the oil and water layers. 
The formation of the scum is no indication of the presence of heavy metals, 
unless the scum is dark in color. 

Oils manufactured in primitive stills or oils improperly stored in metal 
containers (especially if the oils are not thoroughly dried) or oils containing 
large amounts of free acids will often contain heavy metals. Anise, bay, 
sweet birch, cajuput, clove, geranium, and sassafras oils usually contain 
heavy metals when distilled commercially. Therefore, it is well to test 
those oils to ascertain whether or not they have been properly treated to 
remove such impurities. 

A metallic impurity frequently encountered in essential oils is iron. 
Oils distilled using iron condensers and oils stored in imperfectly lined drums 
frequently show the presence of this impurity. Oils rich in phenols, or 
containing a phenol group, such as the salicylates, are often contaminated. 
Iron will not be precipitated by hydrogen sulfide in an acidic medium and, 
therefore, will not give a positive heavy metals test. Ammonium sulfide 
or sodium polysulfide will precipitate black ferrous sulfide. 

The test as described above shows a high degree of sensitivity : ten parts 
per million of metallic Jead in oil of -cloves gives a positive test ; the threshold 
yalue is Approximately fivfc parts per million. 

140 Thirteenth Revision/ 658, 



Removal of Heavy Metals. For the removal of metallic impurities from 
essential oils, citric or tartaric acid is frequently employed, giving rise to 
complex citrates and tartrates which are insoluble and which may be filtered 

Procedure: Add to the oil a small amount of dry tartaric 
acid (usually 1 to 1 per cent will prove sufficient) and shake 
thoroughly. Permit the acid to settle and filter the supernatant 
liquid. If this method should fail to remove all the metallic 
impurities, agitate the oil with $ to 1% of a saturated aqueous 
solution of tartaric acid, separate the oil, shake thoroughly with 
salt, and filter. 

The removal of heavy metals from clove, bay, pimenta, and geranium 
oils frequently requires several treatments. 

When reporting the presence of heavy metals in an oil, it is well to indi- 
cate the relative amount found by terms such as : strongly positive ; positive ; 
positive small amounts; positive traces. 


Dimethyl sulfide occurs as a normal constituent in peppermint oils. 
Upon rectification of the oil obtained by steam distillation from the plant, 
most of this volatile compound is lost be- 
cause of its low boiling point (boiling point 
= 37.5-38). Hence, the presence of dime- 
thyl sulfide in a peppermint oil is an indica- 
tion that such an oil has not been rectified. 
"The United States Pharmacopoeia" 141 has 
made use of the following procedure to assure 
the absence of dimethyl sulfide found in non- 
rectified oils: 

Procedure: Distill 1 cc. from 25 cc. 
of peppermint oil and carefully super- 
impose the distillate on 5 cc. of a 6.5% 
mercuric chloride solution in a test 
tube. A white film does not form at 
the zone of contact within 1 min. 

DIAGRAM 4.12. Apparatus 
for the determination of Di- 
methyl sulfide. 

This test is based upon the reaction of 
dimethyl sulfide with mercuric chloride, giving 

a white sulfonium compound which is insoluble in saturated mercuric chlo- 
ride solution. The following modification 142 of this official test is more sen- 
sitive and somewhat more reliable : 

141 Thirteenth Revision, 390 (Peppermint Oil). 

148 This modification has proved satisfactory during the last five years in the laboratories 
of Fritzsche Brothers, Inp. 


Dry the oil by shaking thoroughly with a small amount of 
anhydrous sodium sulfate in a stoppered bottle and filter. Place 
25 cc. of this dried and filtered oil in a large Pyrex test tube 
(diameter = 22 mm., length = 200 mm.) which is clamped to 
a ring stand at an angle of approximately 45. Add a small 
piece of clay chip. Insert a tight-fitting cork equipped with a 
bent glass tube which extends 2 cm. through the cork. The 
other leg of this bent tube is inserted into a second test tube 
which contains 5 cc. of a 6.5% aqueous solution of mercuric 
chloride (see Diagram 4.12). The tube should not dip into the 
solution, but should extend to within 1 cm. of the surface. 
Apply gentle heat until the oil begins to boil. Heating is con- 
tinued until the ring of condensing vapor rises to within 1 cm. 
of the end of the glass tube. If the oil has been carefully dried 
and the heating has been carried out slowly, no oil will distill 
over into the second test tube. The formation of a white scum 
on the surface of the mercuric chloride solution or on the sides of 
this second test tube indicates the presence of dimethyl sulfide 
in the oil. 


a. Test for Thiophene. Nitrobenzene which has been manufactured 
from an impure grade of benzene will give a positive thiophene test, if 
insufficiently purified. This is due to the fact that inferior grades of benzene 
contain thiophene, SCH : CHCH : CH, and that all thiophene compounds 

give an intense blue coloration when mixed with isatin, CeHUNHCOCO, and 

concentrated sulfuric acid, because of the formation of indophenin, 
(Ci 2 H 7 NOS)x. 

Procedure: 143 Shake thoroughly 5 cc. of nitrobenzene and 0.5 
cc. of concentrated sulfuric acid, in a test tube, and add a pinch 
of isatin, and again shake the mixture thoroughly. Permit the 
test tube to stand for 2 hr. No blue coloration should appear 
during this interval. 

b. Soap Test. The soap test 144 is an empirical method of testing the 
purity of nitrobenzene. Since a large quantity of this synthetic is used to 
perfume soaps, it is necessary to carry out a soap test to determine whether 
or not the nitrobenzene in question will cause a discoloration of the soap. 

Procedure: Into a large, wide Pyrex test tube of approxi- 
mately 75 cc. capacity introduce 5 cc. of the nitrobenzene and 10 
cc. of a 15% aqueous solution of potassium hydroxide. Heat 
the mixture to boiling over an open flame. It is important to 

143 This is a modification of the test described in "A. C. S. Analytical Reagents," Amer- 
ican Chemical Society, Washington, D. C., March (1941), 38. 

144 Gildemeister and Hoffmann, "Die atherischen Ole," 3d Ed., Vol. I, 673. 


shake thoroughly the test tube while the mixture is heated and 
boiled, in order to prevent the formation of two layers. (The 
nitrobenzene and potassium hydroxide solution will then be 
thrown out of the test tube with explosive violence.) After 
boiling for 2 min., permit the test tube to stand, at room tem- 
perature, for one-half hour, and then filter the mixture through 
filter paper previously wetted with water. The potassium hy- 
droxide solution passes through the wetted paper; the nitro- 
benzene is retained. The alkaline filtrate should be colorless, 
or at most show only a light yellow color. A full deep yellow 
indicates that the nitrobenzene has been insufficiently purified 
or is old. Such a product will require rectification before it is 
satisfactory for use in soaps. 


Phellandrene readily yields a solid nitrite which occurs as a voluminous^ 
flocculent precipitate in the following test. 

Procedure:"* Into a test tube introduce a solution of 5 g. of 
sodium nitrite in 8 cc. of water. Superimpose a solution of 5 cc. 
of the oil in 10 cc. of petroleum ether. Add slowly 5 cc. of gla- 
cial acetic acid, shaking the tube gently with a rotatory motion. 
A flocculent precipitate at the junction of the two layers indi- 
cates the presence of phellandrene. 

If large amounts of phellandrene are present, the petroleum ether layer 
will solidify to a gel-like mass. 

The crystals may be separated with a Blichner funnel, and purified by 
filtering, washing with water and methyl alcohol, and finally by dissolving 
the crystals in chloroform and then precipitating with methyl alcohol. Since 
there are eight possible isomers, the melting point has little meaning unless 
the physical isomers are separated. 


To detect the presence of furfural in an oil, the following procedure proves 
satisfactory. It is based on the water solubility of furfural and on the well- 
known color reaction of furfural with aniline in the presence of glacial acetic 

Procedure: Shake thoroughly 100 cc. of the oil with 25 cc. of 
distilled water in a separatory funnel. Permit the mixture to 
stand until a good separation is obtained. Filter the aqueous 
layer through wetted paper to give a clear solution. Add 1 cc. 
of the filtered aqueous layer to 5 cc. of a 2% solution of freshly 
distilled aniline in glacial acetic acid. The presence of small 
amounts of furfural will result in an inytdfise deep red color within 
5 min. If a negative test results, extract thfc filtered aqueous 

144 Wallach and Gildemeister, Liebigs Ann. 246 (1888), 282. 


layer with 25 cc. of ether. Cautiously evaporate the ether on a 
steam bath. Add 1 cc. of distilled water and then 5 cc. of the 
acetic acid aniline solution. The appearance of an intense deep 
red color within 5 min. indicates the presence of traces of 

If a red color is obtained, the furfural may be separated from a fresh 
sample of the oil (following the above procedure), and identified by the 
formation of a suitable derivative. 

If only a small sample of the oil is available, the test may be carried out 
directly on the oil itself. Garratt 146 has suggested the following method for 
the determination of furfural. 

Procedure: To 0.1 cc. of the oil in a test tube add from a 
burette 5 cc. of a 2% solution of freshly distilled aniline in 
glacial acetic acid. Protect from bright light, and allow to 
stand for 10 min. Examine in a Lovibond tintometer, and 
measure the "red value." 

According to this authority, the test may have value for the detection 
of adulteration, if the adulterant has a relatively much higher furfural con- 
tent than the oil to which it has been added, and if the adulterant has not 
been treated to remove the furfural. Garratt tentatively suggests its use 
for the detection of light camphor oil in rosemary oils; of clove oil in bay 
or pimenta berry oils; of Japanese mint oil in American peppermint oil. 147 
It may also have value for the detection of added synthetic methyl salicylate 
to wintergreen and sweet birch oils. 148 

The "ten minute red values" obtained by Garratt 149 for reputedly 
genuine samples of these oils are given in Table 4.15. 


Oil "Ten Minute Red Value" 

Light Camphor 1.8 to 9.2 

Rosemary 0.4 to 0.8 

Clove 23.0 

Pimenta Berry 1.1 

Bay 1.4 

Japanese Mint 4.5 to 7.4 

American Peppermint ca. 0.7 

Methyl Salicylate 0.0 

" Analyst 60 (1935), 369, 371. 

147 This is the basis of the color reaction for the detection of oil of Mentha arvensis (Jap- 
anese mint), in oil of Mentha piperita L. (peppermint oil) ; this test is official in "The United 
States Pharmacopoeia," Thirteenth Rev., 390. It has been the experience of the labora- 
tories of Fritzsche Brothers, Inc., that this test is far from being satisfactory and that the 
test which was official in "The United States Pharmacopoeia," Eleventh Revision, is to be 
preferred. (See also "Detection of Mentha arvensis Oil," p. 343.) 

148 LaWall (Am. J. Pharm. 92 (1920), 891) reports the presence of furfural in wintergreen 
and sweet birch oils, and -its absence in synthetic methyl salicylate. 

), 595. 


The reader is referred to the original literature for further details; a list 
of "ten minute red values" is given for more than 50 different oils by 
Garratt. 160 


Methyl salicylate which has been insufficiently purified will frequently 
contain phenol. The presence of this impurity affects markedly the odor 
and flavor of the synthetic. Hence, it is well to test all samples of methyl 
salicylate for phenol. For routine analyses the following simple procedure 
has proved quite satisfactory : 

Procedure I: Dissolve 5 cc. of the oil in 50 cc. of a 1 N 
aqueous potassium hydroxide solution. Heat on a steam bath 
for 2 hr., cool to room temperature, and acidify with suifuric 
acid (1:3). Cautiously smell the flask for the distinct charac- 
teristic odor of phenol. If no such odor is apparent the sample 
may be considered free of objectionable amounts of phenol. 
If a phenolic "by-note" is observed, the presence of phenol 
should be confirmed by the method of Dodge. (See "Proce- 
dure II.") 

The Dodge method 151 for the detection of phenol in methyl salicylate 
has proved of value as a qualitative method. Attempts have been made to 
convert this method to a quantitative procedure. However, these have 
proved unsatisfactory, particularly when applied to the natural oils of 
sweet birch and wintergreen. 

Procedure II: Into a 100 cc. Pyrex saponification flask in- 
troduce 10 cc. of the oil in question, and add 35 cc. of a 10% 
aqueous solution of sodium hydroxide, measured from a gradu- 
ated cylinder. Connect an air-cooled reflux condenser and heat 
the flask on a steam bath for 2 \ hr. Remove the flask and allow 
it to cool for 15 min. Neutralize the saponified mixture with 
dilute hydrochloric acid (1 : 3) until the solution is distinctly acid 
to blue litmus paper ; this requires from 3.5 to 5 cc. of acid. The 
hydrochloric acid should be added slowly from a burette so that 
no precipitation occurs. Then slowly add from a burette 
enough of a saturated, freshly prepared sodium bicarbonate 
solution to just neutralize the mixture, and then an additional 
0.5 cc. of the sodium bicarbonate solution. Filter into a 500 cc. 
distillation flask and distill with steam, using an efficient trap 
to prevent the mechanical carrying over of any of the solution. 
A 500 cc. Erlenmeyer flask may conveniently be used for this 
trap; the delivery tube from the side arm of the distillation 
flask should extend to within in. of the bottom of the Erlen- 
meyer flask, and the delivery tube from the trap to the con- 

IM Ibid. 

m Drug Markets 24 (1928), 509. 



denser should not extend more than 1 in. below the rubber 
stopper into the flask 152 (see Diagram 4.13). Collect three 5 cc. 
portions of distillate and filter each distillate. Test for the 
presence of phenol by the addition of enough bromine water to 
give a permanent light brown color. If phenol is present to the 
extent of 0.01% or more, a crystalline precipitate of tribromo- 
phenol (melting point, 95) will form within an hour. 

DIAGRAM 4.13. Apparatus for the detection of Phenol in Methyl Salicylate. 

Procedure H is based upon the well-known fact that acids will react to 
form the corresponding sodium salts, but phenols will not form the corre- 
sponding phenolates when treated with sodium bicarbonate solutions. 
Thus the free phenol is steam distilled out of the solution in which is dis- 
solved the nonvolatile sodium salicylate. Normal, pure wintergreen and 
sweet birch oils do not give a positive reaction with this procedure ; certain 
constituents of the oils will distill which are capable of decolorizing the 
bromine water, but which do not form crystalline derivatives under the 
conditions outlined. Hence, a positive test for such oils indicates adultera- 
tion with phenol-containing synthetic methyl salicylate. The test is to be 
considered positive only when definite crystal formation is observed within 1 hr. 
at room temperature in the bromine treated distillates. 


A laboratory distillation of essential oil from plant material is often 
necessary in order to evaluate raw material to be used for large-scale com- 

182 The use of an efficient trap is mandatory to prevent any sodium salicylate from being 
carried over mechanically into the distillate. 


mercial distillations. The determination of the essential oil content is also 
important in appraising the quality of spices and oleoresins. 

Such determinations may be conveniently carried out in a special ap- 
paratus devised by Clevenger. 163 This apparatus offers the following ad- 
vantages: compactness, cohobation of distillation waters, the actual dis- 
tillation and separation of the essential oil (so that certain chemical and 
physical properties may be determined, and so that the odor and flavor of 
the oil may be studied) and an accurate determination of the essential oil 
content using only small quantities of plant material. Furthermore, this 
apparatus may be used to advantage for steam rectification of small amounts 
of essential oils. 

I* 3 cm 


Oils Heavier 
than Water 

DIAGRAM 4.14. 

Apparatus fur the determination of the volatile oil 
content of plant materials. 

The apparatus consists of two specially designed oil traps and a small 
condenser of the "cold-finger" type 154 (see Diagram 4.14). Two traps are 
supplied; one, for oils lighter than water; the other, for oils heavier than 
water. The diagrams are self-explanatory. 

Procedure: Place a sufficient quantity of the ground or 
chipped material 156 to yield 2 to 6 cc. of oil (preferably 4 cc.) in 

Am. Perfumer 23 (1928), 467. 

164 An Allihn type condenser having at least four bulbs is often substituted to prevent 
loss of oil and water vapor. However, if a moderate rate of distillation is maintained, the 
"cold-finger" condenser proves satisfactory, since the thin layer of condensed water forms 
an effective seal. 

166 It is very important that the material be ground or chipped into small pieces, es- 
pecially in the case of woods, roots, and berries. The yield of oil is greatly increased, the 
time required for distillation is materially reduced, and the quality of the resulting oil is 


a round bottom, short-necked flask of 2 liter capacity. Add 
sufficient water to the flask to correspond to 3-6 times the 
weight of the plant material; in general, 4 times the weight is 
sufficient. Attach the proper essential oil trap and the con- 
denser to the flask, and add enough water to fill the trap. 
Place the flask in an oil bath, heated electrically or by a Bunsen 
burner to approximately 130. Adjust the temperature of the 
bath so that a condensate of about 1 drop per sec. is obtained. 
Continue the distillation until no further increase of oil is 
observed. Usually 5 to 6 hr. are sufficient, although in the 
case of the distillation of certain woods and roots a much longer 
period may be necessary. When the distillation has been com- 
pleted, permit the oil to stand undisturbed so that a good sepa- 
ration is obtained, and so that the oil may cool to room tempera- 
ture. Determine the number of cc. of oil obtained, and express 
the yield as a volume/ weight percentage; i.e., number of cc. of 
oil per 100 g. of plant material. 

In the event that a good separation is not obtained, the oil and water 
may be withdrawn from the trap into a graduated cylinder; the addition 
of sufficient salt to saturate the aqueous layer often aids in obtaining a sharp 
separation. Periodic withdrawal of the oil and water into such a cylinder 
is sometimes necessary when the oil being distilled has a specific gravity 
close to that of water, or when the oil consists of two main fractions one 
lighter than water, and the other heavier than water. 

The volume/weight may be converted into a weight/weight relation- 
ship by means of the following formula : 

P = pD 

where: P = wt./wt. percentage; 

p = vol./wt. percentage at temperature t; 
D = density of oil at temperature t. 

This necessitates the determination of the specific gravity of the separated 

It is advisable to permit the separated oil to remain overnight in an 
uncorked bottle before evaluating the odor and flavor. Freshly distilled 
oils often have a peculiar weedy note, which soon disappears. The yield 
and the physicochemical properties of the resulting oil will agree closely 
with the results of a commercial distillation. However, the oil from a com- 
mercial or pilot still is generally superior to that obtained in the Clevenger 
apparatus in respect to odor and flavor. 

improved. The distillation should be carried out immediately after the material has been 
ground to prevent loss of oil by evaporation. The sample to be examined should be repre- 
sentative of the lot or shipment in question. 


When determining the essential oil content of oleoresins, it is best to 
bring the water to incipient boiling before adding the oleoresin 156 and to 
distill at a faster rate. The addition of clay chips and boiling tubes will 
prevent undue bumping. 


The determination of the content of ethyl alcohol in essences, tinctures 
and alcoholic extracts is frequently necessary. Because of the presence of 
volatile esters and essential oils, a determination by distillation alone is 
usually impossible. Consequently these interfering substances must be 
removed by washing with heptane or petroleum ether before such distilla- 
tion is attempted. The two procedures given below give satisfactory results : 

Procedure Method I: Pipette 25 cc. of the sample into a 
500 cc. scparatory funnel, noting the temperature. Add 100 
cc. of a saturated salt solution and 100 cc. of petroleum ether. 
Shake thoroughly for 2 to 3 min., and permit the mixture to 
stand undisturbed until a good separation is obtained (usually 
within 5 to 60 min.). 157 

Draw off the salt solution into a 1 liter distilling flask. 
Wash the petroleum ether layer with two successive 35 cc. por- 
tions of saturated salt solution, adding both washings to the 
solution in the distilling flask. Discard the petroleum ether 
layer. Add 100 cc. water to the contents of the distilling flask; 
also a small amount of solid phenolphthalein and enough 10% 
aqueous sodium hydroxide solution to make the contents alka- 
line to the indicator. Also add a few small clay chips and 
slowly distill until a distillate of about 70 cc. has been collected 
in a 100 cc. volumetric flask immersed in a beaker of cold water 
(use a straight tube water-cooled condenser). Add enough 
distilled water to make the volume up to about 90 cc. If the 
distillate remains water-white (or at most has a faint opalescence 
not a turbidity), adjust the temperature to that originally 
observed and make up to 100 cc. l:>8 

1M The weight of sample can be determined conveniently by placing approximately the 
amount of oleoresin required in a graduate and weighing before and after the sample has been 
introduced into the flask. 

167 If a sharp separation is not obtained pipette a 25 cc. sample into a 1 liter distilling 
flask, add 500 cc. of water and distill. Collect 100 cc. of distillate in a 250 cc. separatory 
funnel, saturate with salt, add 100 cc. petroleum ether, and shake thoroughly. After the 
layers have separated continue as directed in the second paragraph of the procedure. 

The heptane distillation method may also be used (see "Procedure, Method II"). 

168 If a turbid solution is obtained, transfer the distillate completely from the volumetric 
flask with the aid of distilled water into a 250 cc. separatory funnel. Add 50 cc. of petroleum 
ether and shake thoroughly. (It may be necessary to add enough salt to saturate the water- 
alcohol mixture in order to get a sharp separation.) When a sharp separation is obtained 
(this usually takes from 15 to 60 min.), draw off the lower layer into a 1 liter distilling flask. 
Wash the petroleum ether layer successively with a 50 cc. and a 25 cc. portion of saturated 




Determine the specific gravity accurately and, from this, 
the alcohol percentage by volume (see Table 4.16). Multiply 
by 4 to obtain the alcohol content of the original material. If 
this value is above 25%, 159 determine the refractive index at 
20 and compare with the value given in Table 4.17. The 

calculated index should not 
differ by more than 0.0002 
from the experimentally de- 
termined value. A larger 
difference indicates the 
presence of some interfer- 
ing substance in the alco- 
holic distillate. The deter- 
mination should then be 
repeated, using the double 
distillation procedure pre- 
viously described in foot- 
note 158. 

Procedure Method II. 
Into a 500 cc. Erlen- 
meyer flask pipette 25 cc. 
of the sample and add 50 
cc. of distilled water and 
25 cc. of n-heptane. To the 
250 cc. separatory funnel 
add 40 cc. of n-heptane and 
connect the distilling tube 
and reflux condenser as 
shown in Diagram 4.15. 
Heat gently and distill 
slowly until 40 cc. of dis- 
tillate have been collected 

S7 40 <* Mark 

DIAGRAM 4.15. Apparatus for the 
determination of alcohol. 

under the heptane layer in 
the separatory funnel. 
Permit the contents of the 
funnel to stand undisturbed for 15 min. to attain room tem- 
perature and drain the distillate into a 50 cc. volumetric flask. 
Wash the residual heptane with two 4 cc. portions of distilled 
water, adding these washings to the volumetric flask. Fill the 
flask to the mark and determine the specific gravity of the mix- 
ture and calculate the alcoholic percentage by means of Table 

salt solution and add these washings to the distilling flask. Add 100 cc. of water, a small 
amount of solid phenolphthalein, and make alkaline with 10 per cent sodium hydroxide 
solution. Continue as before, collecting a distillate of about 70 w. If a turbid solution is 
again obtained resort to the heptane distillation method (see "Procedure, Method II"). 

159 If the alcoholic percentage is less than 25 per cent, pipette 50 cc. of the distillate into 
a 500 cc. distilling flask, add 100 cc. distilled water, a few clay chips, and distill slowly until 
a distillate of 20 cc. has been collected in a 25 cc. volumetric flask. Adjust the temperature 
and make up to 25 cc. Continue as before, but multiply by 2 (instead of 4) to obtain the 
alcohol percentage in the original material. 




Per Cent of 
CsHtOlI by 
Volume, at 

Per Cent of 
CtHtOlI by 


















































































Specific Gravity 
m Air at 

Specific Gravity 
m Air at 
13 56 






















































































TABLE 4.16. Continued 

Per Cent of 
CjH 4 OH by 
Volume, at 

Per Cent of 
CjHjOH by 

Specific Gravity 
in Air at 

Specific Gravity 
in Air at 
15 56 



















































. 0.9248 



































































































* 70.10 

















TABLE 4.16. Continued 

Per Cent of 
CiHiOH by 
Volume, at 

Per Cent of 
CiIliOH by 

Specific Gra\it> 
in Air at 

Specific Gravity 
m Air at 













































































100 100.00 



4.16. Multiply by 2 in order to obtain the alcohol content of 
the original material. 

It should be noted that certain low boiling, water-soluble constituents, 
such as acetic acid and acetone, will interfere in such a determination. 
However, most low boiling esters are readily absorbed by the heptane layer. 


a. Determination by the Bidweil-Sterling Method. The most con- 
venient method for the determination of water in essential oils, oleoresins, 
and drugs is by the water determination apparatus of Bidwell and Sterling. 160 
The sample to be tested is distilled in this apparatus with a liquid immiscible 
with water, such as toluene. The special trap collects and measures the 
condensed water, the excess solvent overflowing and returning to the still. 

Procedure: Connect the apparatus as shown in Diagram 4.16. 
Introduce into the 500 cc. flask, sufficient material, accurately 
weighed, to yield from 2 to 4 cc. of water. Add about 200 cc. 
of toluene to the flask and also fill the receiving trap with 

160 J. Ind. Eng. Chem. 17 (1925), 147. 



Percentage of Alcohol Refn 
(by Volume) at 15.56 

ictive Index 
a* 20 
t. 34 176 
t. 34666 















16 ... 





21 .. .... 





* These values are based on the Reference Tables of "Methods of Analysis of the 
A.O.A.C.," 4th Ed. (1935), 663-670. 

toluene, poured through the top of the condenser. Heat the 
flask gently by means of a Bunsen burner or electric hot-plate 
until the toluene begins to boil. Distill at a rate of about 2 
drops per sec. until most of the water has passed over. Then 
increase the rate of distillation to about 4 drops per sec. When 
no further increase in collected water is observed, continue the 
distillation for an additional 15 min. Permit the apparatus to 
cool. When the water and toluene have separated completely, 
read the volume of water, and calculate the percentage present 
in the substance. 

If the condenser and moisture trap have been thoroughly cleaned with 
chromic acid cleaning solution, the tendency of droplets to adhere is greatly 
minimized. Should such droplets of water be observed on the sides of the 
condenser, they may be forced down by brushing the inner tube of the con- 
denser with a small brush previously saturated with toluene. 

A convenient method for detecting the presence of dissolved water in 
essential oils, such as rose and bay, has been described under "Solubility," 
see p. 252. 



b. Determination by Karl Fischer Method. For the determination of 
mere traces of water, the method employing the Karl Fischer water titration 
reagent will prove exceptionally sensitive. 

The Karl Fischer water titration reagent 161 is a solution of iodine, sulfur 
dioxide, and pyridine in methyl alcohol. The method depends on the 
oxidation of sulfur dioxide by iodine in the presence of 
water to form sulfuric and hydriodic acid. | [ 

S0 2 + 21 + 2H 2 O -> H 2 S0 4 


The reaction is conducted in the presence of pyridine which 
acts as an acid acceptor, thus enabling the reaction to go 
to completion. The end point is indicated by a color 
change from yellow to reddish-brown, the latter being pro- 
duced by the free iodine in the reagent when an excess of 
the reagent is added. 

The method is applicable to a large number of organic 
and inorganic compounds, both liquid and solid. The 
exact limitations of the method have not been determined, 
but it can probably be used on all organic and inorganic 
compounds that do not react with the reagent and that 
are not naturally colored red or brown. It is known to be 
applicable to organic compounds such as hydrocarbons, 
alcohols, esters, carboxylic acids (except formic), halogen 
derivatives of hydrocarbons, phenols, nitro compounds, 
amines, and heterocyclic compounds. It is not applicable 
to aldehydes and ketones, nor to reducing compounds 
which react readily with iodine in the cold. The active 
hydrogen in primary and secondary amines must be 
blocked by solution in glacial acetic acid before titrating 
with the reagent. 

Liquids are dissolved in a mutual solvent for both the 
sample and the reagent before titrating. Solids may be 
analyzed by pulverizing and dissolving or suspending in dry methyl alcohol. 
It is not essential that the material be soluble in methyl alcohol, as the 
hygroscopic nature of both methyl alcohol and the reagent will act to extract 
the water from the sample. 

The solvent used in preparing the sample for analysis will contain some 
moisture, hence a blank titration must be made using the same volume of 
solvent and the same size flask, as the moisture in the air space is an integral 
part of the blank. To check the end point, breathe into the flask and the 

l Angew. Chem. 48 (1935), 394. 

DIAGRAM 4.16. 
Apparatus for the 
determination- of 


end point will disappear, but an additional drop or two of the reagent should 
bring back the reddish-brown color. The choice of solvents is wide : methyl 
alcohol, dioxane, glacial acetic acid, chloroform, etc. 

When attempting new applications of the method, i.e., with new or 
unknown compounds, the reactivity of the compound with the Fischer 
reagent must first be determined. If the compound is inert toward the 
reagent, the method is applicable. Also, the reagent is so avidly hygro- 
scopic that it will dehydrate hydra ted compounds. The degree of such 
dehydration (number of mols of water reacting with the reagent) must be 
determined beforehand. 

All apparatus must be thoroughly dried and every precaution must be 
made to exclude atmospheric moisture during the titration. The titration 
is carried out in a small flask (125 cc. Erlenmeyer) and taken to completion 
rapidly. This method will detect, in general, 0.0005 g. of water, equivalent 
to 0.005 per cent when using a 10 g. sample. 

Procedure: Pipette 10 cc. of methyl alcohol into each of 
three 125 cc. glass stoppered Erlenmeyer flasks, which should be 
kept stoppered as much as possible. Weigh accurately from 
a weighing pipette about 0.1 g. of distilled water into each flask. 
Titrate with the Karl Fischer reagent to the color change (the 
color should change from a straw yellow to a reddish-brown 
when the end point is reached). At the same time run a blank 
on the methyl alcohol. Calculate the water equivalent of the 
reagent by means of the following formula : 


A - B 

where: E = water equivalent of the reagent (in grams of water 

per cc.) ; 

w = weight in grams of water used ; 
A cc. of reagent used for the determination ; 
B = cc. of reagent used for the blank. 

Into a 125 cc. Erlenmeyer flask weigh a sufficiently large sample 
of the material to be tested to yield approximately 0.1 g. of 
water. Add 10 cc. of methyl alcohol and titrate. Run a blank 
at the same time on the alcohol. The water content may be 
calculated from the following formula : 

T> * f . 

Percentage of water 

where: A cc. of reagent used for the determination; 
B = cc. of reagent used for the blank ; 
E water equivalent of the reagent ; 
w weight of sample in grams. 

It is necessary to standardize the reagent daily. 


The Karl Fischer water titration reagent may be purchased from chem- 
ical supply houses, or may be prepared in the following way : 

Place 1 liter of dry methyl alcohol and 400 cc. of pyridine 
in a 2 liter reservoir of an automatic burette. Add 127 g. of 
iodine, stopper the bottle and swirl until the iodine is completely 
dissolved. Cool the bottle in a salt-ice mixture for one-half 
hour and then add 100 g. of sulfur dioxide, 162 weighing by differ- 
ence on a balance. The resulting solution is very hygroscopic 
and must be kept stoppered as much as possible, Then remove 
the bottle from the ice bath and insert the siphon and burette 
unit. Thoroughly grease the ground glass joint between the 
bottle and burette to give an airtight seal. Fit a calcium chlo- 
ride drying tube to the opening at the top of the burette and 
between the bottle and hand aspirator, which is used to fill the 
burette. The tip of the burette is fitted with a 2-hole rubber 
stopper which fits the neck of the 125 cc. Erlenmeyer flask. 
Protect the tip of the burette when not in use. 

It is best to age the solution for two to four days before using so that the 
variation in standardizing from day to day will be minimized. 


Oil of rose contains as a natural constituent a mixture of solid paraffinic 
hydrocarbons known collectively as "stearoptene." The highly purified 
stearoptene is odorless and hence contributes little to the odor value of the 
oil. However, for many years the quality of rose oils was judged super- 
ficially by the "melting point" of the oil; oils with high "melting points" 
were assumed to be unadulterated. As a consequence there arose the 
practice of adding spermaceti, tristearin, high melting paraffins, and guaiac 
wood oil as adulterants. 

"The United States Pharmacopoeia" 163 requires a certain minimum 
content of stearoptene and describes a limiting test for its determination. 

Procedure I: Introduce 1 cc. of oil of rose into a 25 cc. glass- 
stoppered, graduated cylinder and add 1 cc. of chloroform: a 
clear solution should result. Then add 19 cc. of 90% alcohol 
(by volume) : crystals of stearoptene should crystallize out of 
the solution within 24 hr., the temperature being maintained 
at 25. 

A rough indication of the amount of stearoptene present in the oil can 
be obtained by this modified official test. Oils with high stearoptene con- 
tents will deposit an abundant amount of crystalline material immediately ; 
oils with low stearoptene contents will sometimes separate only one or two 

lw Dry the sulfur dioxide by bubbling through concentrated sulfuric acid. Commercial 
sulfur dioxide of refrigeration grade is sufficiently pure for the preparation of the reagent. 
1M Thirteenth Revision, 456. 


well-formed crystals after standing 24 hr. ; some oils will show no separation 
of crystals whatsoever. The appearance of the crystals is also important ; 
only through experience will an essential oil chemist be able to draw con- 
clusions as to possible adulteration from the appearance of the separated 

This test will also indicate whether or not the oil has been properly 
dried; a cloudy solution in one volume of chloroform is usually indicative 
of the presence of water in the oil. 

For the determination of the amount of stearoptene, the oil is usually 
dissolved in dilute alcohol and chilled; the relatively insoluble paraffins 
separate out and can be filtered off and weighed. It is customary to use 
75 per cent alcohol 164 for this determination, although certain investigators 
have recommended the use of 85 per cent alcohol 166 or acetone. 166 

Procedure II: Dissolve 5 g. of the oil in 50 cc. of 75% alcohol 
(by volume) with the aid of gentle heat if necessary. Cool the 
solution in an ice bath at for 2 hr. and filter off the separated 
stearoptene with suction, using a well cooled Blichner funnel. 
Wash the stearoptene with a 50 cc. portion of 75% alcohol 
cooled to 5. Remove as much of the alcohol as possible by 
suction, and then transfer the cake of stearoptene to a tared 
evaporating dish. Break up the cake with a spatula and dry 
in a desiccator for 24 hr. Weigh, and calculate the percentage 
of stearoptene present in the original oil. 

To be assured of the absence of adulterants, it is necessary to examine the 
separated stearoptene. 

The naturally occurring paraffinic hydrocarbons in rose stea^optene 
consist of at least two components 167 having melting points of 22 and 4 1 . 168 
The mixture separated from rose oil should melt between 32 and 37; 
usually at about 33 34. l69 Additions of spermaceti, guaiac wood oil, and 
many readily available solid paraffins will raise the melting point. 

Spermaceti, tristearin, or other fatty acid esters may be detected by 
an abnormally high ester number of the separated stearoptene. Occasion- 
ally it is possible to isolate the fatty acids from the saponified material. 

Guaiac wood oil consists mainly of the alcohol, guaiol ; its presence will 
be revealed by a high ester number after acetylation of the separated stearop- 

w* Ber. Schimmel & Co., April (1889), 37. 

166 Burgess, "Chemistry of Essential Oils and Artificial Perfumes" (Parry), D. Van 
Nostrand Co., Inc., New York, 1921, 402. 

168 Jeancard and Satie, Bull. soc. chim. [3] 31, (1904), 934. 

187 FlUckiger, "Pharmakognosie," 3d Ed., 170. 

188 Gildemeister and Hoffmann, "Die atherischen Ole," 3d Ed., Vol. I, 302. 

189 Parry, "Chemistry of Essential Oils and Artificial Perfumes," D. Van Nostrand Co., 
New York (1921), 402. 


High melting paraffins are very difficult to detect when used as adulter- 
ants for rose oils. The appearance of the stearoptene may reveal their 
presence; a peculiar granular structure is frequently indicative of such 
additions. The appearance of the crystals which separate in the test de- 
scribed under Procedure I is sometimes helpful in this connection. 

The congealing point of the rose oil itself is also indicative of the amount 
of stearoptene present in the oil. The congealing point of rose oil 170 has 
been defined as that temperature at which the first crystals appear when the 
oil is subjected to slow cooling. (This is quite different from the true con- 
gealing point of oils such as anise. See "Congealing Point/' p. 253.) De- 
termine the "congealing point" of the oil by the following technique: 

Procedure III: Place 10 cc. of the oil in a test tube having a 
diameter of 15 mm. ; suspend a thermometer in the oil in such a 
way that it touches neither the sides nor the bottom; warm the 
contents of the tube to about 5 above the point of saturation; 
stir well; then permit the oil to cool slowly until the first crys- 
tals appear; read the temperature. Repeat the determination. 

As a general rule, good Bulgarian oils produced by the usual methods 171 
show a congealing point of 18 to 23. l72 


The congealing point of sassafras oils gives a good estimate of the safrole 

Procedure: Determine the congealing point of the sassafras 
oil (see p. 253 for details), and estimate the safrole content from 
Table 4.18. 


Per Cent Safrole Congealing Point 

100 11.0 

90.. 7.5 

80 4.6 

70 1.7 

GO -1.3 

Table 4.18 173 will give values of the safrole content with an accuracy of 
about 2 per cent if the congealing point is above 2. 

170 Raikow, Chem. Ztg. 22 (1808), 149. 

171 Pure Bulgarian oils of exceptionally fine quality produced by rotary distillation 
allowed congealing points as low as +13. (See also Guenther and Gamier, Am. Perfumer 
25 (June-December 1930).) 

172 Gildemoister and Hoffmann, "Die atherischcn Ole," 3d Ed., Vol. II, 837. 

173 This table was prepared by the laboratories of Fritzsche Brothers, Inc.; it is based 
on the congealing points of known mixtures of safrole and pinene and safrole and eugenol. 



For the determination of cedrol in cedarwood oils, Rabak 174 has suggested 
the following method : 

One hundred parts of oil are agitated vigorously with 6 
parts of 65% alcohol (by volume) for one to two minutes in a 
widemouthed, stoppered flask. Sudden and complete solidifi- 
cations of the emulsion thus formed usually result if the oil 
contains a sufficient quantity of cedrol. If it fails to solidify, 
add a small quantity of crystalline cedrol to the emulsion, and 
cool in a refrigerator for several hours. Filter the solidified 
mass with the aid of a well cooled Blichner funnel and wash the 
fine silky crystals <vith a few drops of cold 98% alcohol. Weigh 
the dry crystals. The cedrol may be purified by dissolving it 
hi hot alcohol, then cooling and filtering the mass. 

In general, an analytical method based upon the actual separation of a 
constituent by physical means will not give completely accurate results. 
However, comparative data may be obtained provided all experimental 
conditions are carefully controlled. 

This method appears to be of value only for obtaining comparative data 
when two oils are examined simultaneously; all experimental conditions 
should be maintained as identical as possible. 


In order to standardize the color of oleoresin capsicum it has been found 
that a very close match to the natural color can be attained with the proper 
mixture of solutions of potassium dichromate and cobalt chloride. The 
color standard is prepared as follows : 

Into a 50 cc. Nessler tube pipette 5 cc. of a 0.1 N potassium 
dichromate solution 175 (4.904 g. K 2 Cr 2 07 per liter) and 0.5 cc. 
of a 0.5 N cobaltous chloride solution (5.948 g. CoCl 2 -6H 2 per 
100 cc.) and make up to 50 cc. with distilled water. 

The color value of the oleoresin is defined as the number of cc.'s of ace- 
tone, multiplied by 100, which are necessary to add to 1 cc. of a 1 per cent 
solution of the oleoresin capsicum in acetone, in order to match the color 
standard as outlined above. The height of the liquid in the Nessler tube 
should be about 8 in. and the color should be matched by looking down into 
the column, and not laterally. 

Procedure: Weigh accurately 1.00 g. of oleoresin and make 
up to 100 cc. with acetone. Pipette 1 cc. of this 1 % solution 

174 Am. Perfumer 23 (1929), 727. 

175 The potassium dichromate and the cobalt chloride used for these solutions should be 
of the grade known as "analytical reagent." 


into a 50 cc. volumetric flask and make up to 50 cc. with ace- 
tone. 176 Pour this dilute solution (0.02%) into a burette. In- 
troduce sufficient of this solution into an empty 50 cc. Nessler 
tube to approximate the color of the standard (viewed through 
the length of the tube). Then add sufficient acetone to bring 
the volume up to about 4*5-47 cc. and make the final adjustment 
of color by addition of small amounts of the dilute solution 
(0.02%) from the burette. Finally add sufficient acetone to 
bring the volume to exactly 50 cc. and check the color match. 
Color value 

nn [ ^ ~~ (0-02) (no. of cc. of dilute solution required) 1 
L (0.02) (no. of cc. of dilute solution required) J 

Using this procedure, an accuracy of about rt 1,000 units can be obtained. 
The color values will vary between 5,000 and 25,000 for commercial oleo- 
resins; a value of 14,000 is generally considered very satisfactory. 

The procedure may be modified to permit the use of 100 cc. Nessler 
tubes and the colors of the standard, and the solution of oleoresin may be 
accurately matched with a Nesslerimeter. 



For a rapid evaluation of the quality of sweet birch and wintergreen 
oils, the alkali solubility test often proves of value. (See also "Solubility," 
p. 252.) 

Procedure: 117 Introduce 2 cc. of the oil in a 25 cc. glass- 
stoppered, graduated cylinder and add 23 cc. of an aqueous solu- 
tion of potassium hydroxide prepared by dissolving 6.5 g. of 
potassium hydroxide (analytical grade) in sufficient distilled 
water to yield 100 cc. of solution. Shake thoroughly and permit 
the cylinder to stand undisturbed for 24 hr. : no oily separation 
should result, although a separation of a solid waxy material is 
indicative of a normal oil. 

Since the natural waxy separation melts at a relatively low temperature, 
care should be exercised in interpreting the results of this test in warm 

It is well to study the odor of the solution or any insoluble portion. 
Since the potassium phenolate of methyl salicylate is practically odorless, 
additions of foreign, odor-bearing substances may be detected. 

I7e This procedure is satisfactory for oleoresins with a color value of 4,900 or higher ; 
if the color value is lower, a stronger solution should be used. 

177 This is a slight modification of the test described in "The United States Pharma- 
copoeia," Tenth Revision, 239. 



a. Oleum Test. The saturated paraffinic hydrocarbons, found in 
petroleum oils, are chemically very inert ; they are not destroyed by fuming 
sulfuric acid. Other compounds are attacked, giving rise to reaction prod- 
ucts which are soluble in sulfuric acid. 

Procedure: 178 Place 20 cc. of fuming sulfuric acid in a dry 
cassia flask 179 of 150 cc. capacity, and cool thoroughly in an ice- 
salt mixture. Add slowly 5 cc. of the oil in question from a 
small burette. The oil should be added drop by drop, with 
frequent shaking and cooling in the ice-salt mixture, since too 
rapid addition of the oil is apt to cause the liberated sulfur di- 
oxide to carry part of the acid and oil out of the flask. After 
the oil has been added, the flask is again shaken and permitted 
to stand at room temperature for 10 min. It is then warmed 
on a steam bath for 5 min. with frequent agitation. The flask 
is permitted to cool to room temperature and is then filled with 
95% sulfuric acid. After standing overnight, the mineral oil 
will rise into the neck and separate as a colorless, or straw- 
colored liquid. As a confirmatory test, a small amount of the 
separated mineral oil may be removed from the cassia flask (by 
means of capillary action, using a glass tube drawn out to a 
small tip). The refractive index of this separated oil should be 
less than 1.4400. 

A flavor test often will prove of value for the detection of kerosene. In 
this connection, see the discussion of adulteration of "Orange Oils of French 
Guinea/' Vol. III. 

Since petroleum fractions often contain aromatic and unsaturated com- 
pounds as well as paraffins, the separation of the paraffinic portion described 
above does not usually represent the total amount of added petroleum. In 
general, such actual separation usually is a small percentage of the adulterant. 

The test may be rendered more sensitive by preliminary fractionation 
of the oil. 

The addition of petroleum fractions to an oil causes a lowering of the 
specific gravity, index and optical rotation. The solubility of the oil usually 
is affected : this is the basis of the well-known Schimmel Test for citronella 
oils described below. 

b. Schimmel Tests. 

The "Old Schimmel Test." 1 In order to limit the amount of adultera- 
tion of citronella oils with petroleum fractions, the chemists of Schimmel 

178 This procedure is essentially the Oleum Test of "The National Formulary," Eighth 
Edition, 643 (Turpentine Oil). 

179 A narrow necked Babcock bottle may be used in place of the cassia flask; this offers 
the further advantage of permitting the bottle and contents to be centrifuged for better 

Ber. Schimmel & Co., October (1889), 22; (1917), 14. 


nd Company introduced the well-known Schimmei Test. Several modifi- 
ations of this test have been proposed, but the trade accepts the following 
rocedure in writing contracts for oils. 

Procedure: Into a glass-stoppered, graduated cylinder intro- 
duce exactly 1 cc. of the oil. Add dropwise 80% alcohol until 
a clear solution results. This should occur at 1 to 2 volumes. 
Add sufficient 80% alcohol to bring the amount of added alcohol 
to 10 volumes. The solution may show a slight opalescence, 
but should not separate oily droplets even after standing for 
several hours. When adding the alcohol, violent shaking 
should be avoided to prevent an emulsion that will separate only 
after very prolonged standing. 

A oitronella oil meets the Schimmei Test if it yields a clear solution in 
to 2 volumes of 80 per cent alcohol and does not separate oily droplets when 
he amount of alcohol added is increased to 10 volumes. This test limits 
he amount of added petroleum fractions to about 10 per cent. If more than 
his amount has been added, oily droplets will form on the surface of the 
ileoholic solution. Additions of fatty oils will result in the formation of 
>ily droplets which settle to the bottom. 

The "New Schimmei Test." 1 * 1 At a later date the description of the 
original test was modified resulting in the so-called "New Schimmei Test." 
This test is somewhat more stringent than the "Old Schimmei Test" de- 
icribed above. However, the trade has not accepted the new version. A 
lescription of this test follows: 

Oil of oitronella Ceylon must be clearly soluble in from 1 to 2 
volumes of X0% alcohol by volume at 20. Upon the further 
addition of alcohol of the same strength, the solution should 
show an opalescence at the most, but no turbidity or direct 
cloudiness. The alcohol must be added slowly, drop by drop; 
the addition being at once interrupted if a cloudiness or tur- 
bidity appears. The alcohol is then added slowly, drop by 
drop, until the point of highest or maximum cloudiness or 
turbidity is obtained. The mixture is carefully set aside and 
maintained at 20 to observe if any oily constituents separate 
out. Ten volumes of 80% alcohol at the most are added. If 
oil separates out immediately or after prolonged standing, the 
oil does not pass the "New Schimmei Test." Strong or violent 
shaking must be avoided since any possible oily separation will 
become finely dispersed and will not separate out on standing. 

Many oils will show an oily separation at the point of highest cloudiness 
)r turbidity, but will show no oily separation if 10 volumes of 80 per cent 
ilcohol are added. 

181 Ber. Schimmei & Co. (1923), 18. 


The "Raised Schimmel Test" 1 ** In order to limit adulteration with 
mineral spirits to 5 per cent, the "Raised Schimmel Test" was introduced. 
This test has never attained commercial importance. 

Oil of citronella Ceylon is mixed with 5% of kerosene and 
the "Old Schimmel Test" is applied, disregarding any inter- 
mediate stages of cloudiness or turbidity; i.e., simply add 80% 
alcohol up to 10 volumes. A fresh unadulterated citronella oil 
will show no oily separation. Oils containing small amounts of 
petroleum will show an oily separation either immediately or 
after prolonged standing at 20. 

This test is by far the most stringent of the three. 


In testing for rosin as an adulterant in oils, the following pertinent 
properties of this substance should be borne in mind. It is a nonvolatile 
material, and consequently may be concentrated in the residue by distilla- 
tion of the oil under vacuum or at atmospheric pressure ; it is found also in 
the evaporation residue. Rosin consists primarily of complex acids and, 
therefore, will increase the acid number of an oil or of the evaporation residue 
if such residue normally consists of solid esters or paraffins ; this is specifically 
of importance in the case of citrus oils. Rosin is soluble in most organic 
solvents, including petroleum ether, benzene, and xylene; since cinnamic 
aldehyde (the main constituent of cassia oil) is practically insoluble in 
petroleum ether, this permits a convenient separation of added rosin for 
this oil, and is the basis of "The United States Pharmacopoeia" test de- 
scribed below. Rosin gives a dark green copper salt when treated with 
cupric acetate ; this salt is sufficiently soluble in petroleum ether to impart 
to this solvent a green color. Rosin is a relatively high melting solid, 
normally a hard, noncrystalline material which fractures readily ; hence the 
consistency of the evaporation residue is frequently altered if rosin is 

a. Detection of Rosin in Balsams and Gums. 

Procedure: 193 Place in a small mortar 1 g. of the substance, 
powdered or crushed if necessary, and add 10 cc. of purified 
petroleum ether. Triturate well for 1 or 2 min. Filter into a 
test tube and add to the nitrate 10 cc. of a freshly prepared aque- 
ous solution of cupric acetate (1 g. in 200 cc.). Shake well and 
allow the liquids to separate. The petroleum ether layer should 
not show a green color. 

. Schimmel & Co., April (1904), 29; April (1910), 32; April (1911), 47. 
xhe United States Pharmacopoeia," Thirteenth Revision, 688. 


b. Detection of Rosin in Cassia Oils. 

Procedure 7: 184 Shake about 2 cc. of the oil in a test tube 
with 10 cc. of petroleum ether. Permit the liquids to separate 
and decant the benzene layer into a second test tube. Add an 
equal volume of cupric acetate solution (1 in 1000); a green 
color indicates the presence of rosin in the oil. 

It is well to carry out simultaneously a test with an oil known to be free 
of rosin, to act as a blank. Unfortunately, tests based upon color reactions 
have not proved too reliable in mixtures as complex as essential oils ; never- 
theless, this test will give an indication of the presence or absence of rosin. 

Procedure //: 185 About 50 g. of the oil, accurately weighed, 
are distilled from a tared distilling flask over an open flame. 
Continue the distillation until decomposition is evidenced by 
the formation of white fumes within the flask; this usually 
occurs at a temperature of about 280. Cool the flask and 
weigh ; calculate the percentage of residue. 

This test will reveal adulteration with nonvolatile material such as rosin, 
if large amounts have been added. Normal oils show a distillation residue 
of 6 to 8 per cent, or at most 10 per cent, according to Gildemeister and 
Hoffmann. 186 Furthermore, the residue should be tacky, but not hard and 
brittle. According to Allen, 187 formerly of Hongkong, the residue should 
not be higher than 5 per cent for a pure oil. Treff 188 has pointed out that 
distillation should be carried out rapidly, since the amount of residue ob- 
tained is greatly dependent upon the rate of distillation. 

Procedure III: Determine the acid number of the oil in the 
usual manner. If the oil is pure and has been properly stored, 
the acid number should not be greater than 15. 

c. Detection of Rosin in Orange Oils. 

Procedure: Determine the evaporation residue in the usual 
manner. In the case of pure oils this residue upon cooling 
should be soft and waxy, not hard, brittle or tacky. The acid 
number of the residue should lie between 11 and 28, the ester 
number between 118 and 157. 189 

184 "The United States Pharmacopoeia," Thirteenth Revision, 132. 
1M Ber. Schimmel & Co., October (1889), 15. Gildemeister and Hoffmann, "Die athe- 
rischen Ole," 3d Ed., Vol. II, 631. 

i "Die atherischen Ole," 3d Ed., Vol. II, 631. 

187 D. Allen, private communication. 

188 Z. angew. Chem. 39 (1926), 1308. 

189 Gildemeister and Hoffmann, "Die atherischen Ole/' 3d Ed., Vol. Ill, 79. These 
data apply to Italian orange oils. However, the values for oils from other origins do not 
appear to differ materially from these limits. 



It has been pointed out in the "Determination of Esters" that certain 
esters are not completely saponified under the standard analytical condi- 
tions if the time of reflux is limited to 1 hr. Terpinyl acetate is such an 

Additions of esters of this type to readily saponifiable esters (such as 
linalyl acetate) will be revealed by a difference in the ester numbers obtained 
by saponification for periods of 1 and 2 hr., respectively. Under standard 
conditions linalyl acetate is completely saponified in a period of 30 min.; 
terpinyl acetate requires about 2 hr. Hence, an appreciable difference 
between the ester numbers determined after heating for 30 min. and for 
1 hr. (or 2 hr.) indicates the presence of certain foreign esters, such as 
terpinyl acetate, in oils containing only readily saponifiable esters (e.g., 
bergamot oil and lavender oil). If only small amounts of terpinyl acetate 
have been added, the difference will be too small to draw any definite con- 
clusions. However, by modifying the experimental conditions, such small 
differences may be greatly magnified. The method outlined below is the 
classical method developed by the chemists of Schimmcl and Company 190 
for the detection of terpinyl acetate as an adulterant in bergamot oils ; it is 
also applicable to lavender oils and to synthetic linalyl acetate. With further 
modification, it can be used for the detection of terpinyl acetate and terpineol 
in numerous oils; such applications, however, should be made with discretion. 

Procedure: Pipette 2 cc. of the oil into each of three tared 
saponification flasks and weigh accurately. To flask I add 10 
cc. of 0.5 N alcoholic sodium hydroxide solution and 25 cc. of 
alcohol. To flask II add 20 cc. of the alkali solution, but no 
alcohol. To flask III add 10 cc. of the alkali solution and 5 cc. 
of alcohol. (The alkali solution should be measured accurately 
from a burette or pipette.) The contents of flask I and flask 
III are refluxed on a steam bath for a period of 1 hr. ; the con- 
tents of flask II, for 2 hr. Calculate the ester numbers for the 
three determinations. 

In the case of pure bergamot oils, the difference between ester number I 
and ester number II will not be greater than 5; the usual value lies below 3. 
In the case of an oil adulterated with 4 per cent terpinyl acetate, the differ- 
ence amounts to about 10.0; with 10 per cent terpinyl acetate, about 19. 0. m 
Furthermore, in the case of pure oils, ester number III will be approximately 
the arithmetical mean of ester number I and ester number II. 

For oils containing larger amounts of ester, the size of the sample must 
be reduced; 1 cc. will often prove sufficient. In the case of synthetic linalyl 

. Schimmel & Co., October (1911), 115. 
. Schimmel & Co., October (1911), 115. 


acetate, a 1 cc. sample should be used and the quantities of alkali should be 

Fractional saponification may also be used to detect the presence of 
terpineol by carrying out the determination on an acetylized oil ; great dis- 
cretion must be used, however, since terpineol and certain difficultly saponifi- 
able esters may be present as natural constituents, or the process of acetyla- 
tion may result in the formation of such esters. Recourse to fractionation 
of the oil or of the acetylized oil with subsequent fractional saponification of 
the proper fraction may frequently prove of value. Table 4.19 gives the 
boiling points of terpineol and terpinyl acetate at various pressures : 

TABLE 4.19 

Boiling Point 

Pressure in Mm. of Hg. a-Terpineol* Terpinyl Acetate 

5 92.4 90-94t 

10 104.0 110-115t 

760 217.5 220t 

* von Rechenberg, "Einfache und fraktionierte Destination in Theorie und Praxis," 
Schimmel & Co., Miltitz, Leipzig (1923), 257. 

t Gildemeister and Hoffmann, "Die atherischen Ole," 3d Ed., Vol. I, 647. 
J Bouchardat and Lafont, Ann. chim. phys. [6] 9 (1886), 515. 


The addition of turpentine oil as an adulterant generally reduces the spe- 
cific gravity and affects the solubility and optical rotation of most essential 
oils. Its presence may be proved in oils which contain no pinene as a 
natural constituent by the separation and identification of a-pinene, the 
main constituent of turpentine oils. 

Highly purified rf-a-pinone has the following properties: 

Boiling Point = 155-156 

Specific Gravity at 15 = 0.864 

Refractive Index at 20 = 1.4656 

Specific Rotation = + 4824' 

Solubility at 20 4 vol. of 90% alcohol and more. 

The boiling point of a-pinene lies below that of most of the terpenes and 
oxygenated constituents found in essential oils. Consequently, in testing 
for the presence of pinene it is customary to fractionate the oil, collecting 
the first 10 per cent, or better the distillate coming over below 160 at 
atmospheric pressure. 

Procedure: Distill a 50 cc. sample of the oil from a three 
bulb, 125 cc. Ladenburg flask, collecting only the first 5 cc. 

192 The procedure as given is essentially the official method of the Association of Official 
Agricultural Chemists, 6th Ed., 374, for the detection of pinene in orange and lemon oils. 


Mix this distillate with 5 cc. of glacial acetic acid and cool to 
in a freezing bath. Add 10 cc. of amyl nitrite and then add 
dropwise, with constant stirring, 2 cc. of dilute hydrochloric 
acid (2:1). Permit the mixture to stand in the freezing bath for 
15 min. arid collect the crystals which form on a Biichner funnel. 
Wash thoroughly with alcohol. Permit the crystals to dry at 
room temperature and dissolve in a small amount of chloroform. 
Add methyl alcohol to the chloroform solution dropwise until 
the nitrosochlorides precipitate out. Separate the crystals by 
filtration and dry at room temperature. Mount in a fixed oil 
(olive oil) and examine microscopically. Pinene nitroso- 
chloridc 193 crystals have irregular pyramidal ends (melting 
point, 103). 


The acetic acid esters of glycerin are occasionally employed as adulterants 
in order to increase the apparent ester content. Since all three acetins are 
relatively soluble in water they may easily be washed out and tested for by 
the procedure described below. The least soluble of the three is triacetin; 
even this, however, is soluble in water to the extent of about 7 per cent. 
In order to insure the removal of most of the triacetin, a 5 per cent alcoholic 
solution is employed. 

Procedure: 194 Shake 20 cc. of the oil with 40 cc. of 5% alcohol 
in a 125 cc. glass-stoppered, separatory funnel. When the 
mixture has separated completely withdraw 30 cc. of the alco- 
holic solution by means of a pipette and place it in a 125 cc. 
Erlenmeyer flask. Neutralize the solution with 0.5 N sodium 
hydroxide, using a 1% phenolphthalein solution as indicator. 
Then add exactly 5 cc. of 0.5 N alcoholic sodium hydroxide and 
heat the mixture on a steam bath for 1 hr. Remove the flask 
and allow the mixture to cool. Titrate the excess of alkali with 
0.5 N hydrochloric acid. At least 4.7 cc. of the acid should 
be used for this neutralization. 

This test is not specific for acetins; if large amounts of other water- 
soluble esters are present, these will appear in the dilute alcoholic layer. 


Alcohol has been used frequently as an adulterant, since it is a cheap 
and available diluent for essential oils. The presence of ethyl alcohol as an 
adulterant may be readily detected by several simple tests. 

193 Limonene nitrosochloride*, which may also be present, crystallizes in needles. 

194 The procedure as given is essentially that of "The United States Pharmacopoeia," 
Thirteenth Revision, 285, described under Oil of Lavender. , 


Procedure I: Determine accurately the refractive index and 
specific gravity of the oil. Then shake thoroughly an equal 
volume of oil and saturated salt solution in a separatory funnel. 
Permit the oil to separate completely and determine the refrac- 
tive index and specific gravity of this washed oil. These should 
not differ materially from those of the original oil. An ap- 
proximation of the amount of added alcohol may be obtained 
from a consideration of these values. 

This procedure is not specific for alcohol and will detect other water- 
soluble adulterants. 

Procedure II: Place 50 cc. of the oil (previously dried with 
anhydrous sodium sulfate) in a 100 c. Ladenl>u;g flask and 
distill slowly over an open flame. Collect and measure the 
distillate below 100. Since most constituents of essential oils 
boil much above 100, unadulterated oils generally show no 
distillate at this temperature. However, if a distillate is ob- 
tained dilute to 10 cc. with distilled water. Test a 5 cc. portion 
for ethyl alcohol by the iodoform test and the residual 5 cc. 
portion by the ethyl benzoate test. 

Iodoform Test: To 5 cc. of the diluted distillate add 10 drops 
of a 10% sodium hydroxide solution and suflicient iodine- 
potassium iodide solution drop by drop until a faint, permanent 
yellow color is obtained, indicating an excess of iodine. Allow 
the test tube to stand undisturbed for 5 min. The formation of 
yellow, flat, hexagonal crystals with tiie peculiar odor of iodo- 
form indicates a positive reaction. If no positive result is 
obtained, heat the test tube to 60 for 1 min. in a beaker of 
water and permit the mixture to stand for 1 hr. 

The iodine-potassium iodide solution is prepared by dis- 
solving 2 g. of potassium iodide in 8 cc. of distilled water and 
adding 1 g. of iodine; stir until solution is complete. 

Ethyl Henzoate Test: To 5 cc. of the dilute distillate add 5 
drops of benzoyl chloride and 2 c. of a 10% sodium hydroxide 
solution. Warm on a steam bath. The fruity odor of ethyl 
benzoate indicates the presence of ethyl alcohol. 

The iodoform test will give a positive reaction with any compound con- 


taming a CHsC group united to either a carbon or a hydrogen atom, or 
to any chemical which is oxidized under the conditions of the test to a com- 
pound having such a structure. In particular, acetone will give a positive 
iodoform test. In the ethyl benzoate test, all low boiling aliphatic alcohols 
will give fruity odors. However, only ethyl alcohol will give positive results 
with both the iodoform and ethyl benzoate testp. 

The presence of ethyl alcohol materially lowers the flash point of most 
essential oils. There exist insufficient published data on the normal limits 


of the flash points of the unadulterated oils to draw valid conclusions from 
the results of flash-point determinations. 

Oils containing relatively large amounts of alcohol will form milky emul- 
sions with water. Use of this fact may be made for a quick test. 


The following procedure is based upon the fact that methyl alcohol may 
readily be oxidized to formaldehyde by potassium permanganate in the 
presence of dilute phosphoric acid. The resulting formaldehyde can then 
be detected by means of the reaction with chromotropic acid (1,8-dihydroxy- 
naphthalene-3,6-disulfonic acid) which gives a violet color in the pjfcsence 
of sulfuric acid. The chemistry of this color reaction is unknown. 

The following compounds give no reaction with chromotropic acid: 
acetaldehyde, aromatic aldehydes, butyraldehyde, chloralhydrate, croton- 
aldehyde, glyoxal, isobutyraldehyde, isovaleraldehyde, oenanthal, pro- 
pionaldehyde. Fructose, furfural, glyceraldehyde, robinose and sucrose all 
give yellow colors. Other sugars, acetones and carboxylic acids do not 
react. High concentrations of furfural give red color. 

This test is satisfactory for the detection of methyl alcohol in the presence 
of ethyl alcohol. 

Procedure : 195 Mix 2 drops of the alcohol in question in a test 
tube with 2 drops of 5% phosphoric acid and 2 drops of 5% 
potassium permanganate solution. After 1 min., add a little 
solid sodium bisulfite with shaking until the mixture is de- 
colorized. If any brown precipitate of the oxide of manganese 
remains undissolved, add a further drop or two of phosphoric 
acid and a little more sodium bisulfite. When the solution is 
entirely colorless, add 8 cc. of 72% sulfuric acid and a small 
amount of finely powdered chromotropic acid. Shake the 
mixture well and then heat to 60 for 10 min. A violet color 
which deepens on cooling, indicates the presence of methyl 

According to Feigl the identification limit is 3.5 y methyl alcohol; the 
concentration limit, 1 : 13600. 


a. Detection of Various Esters. Relatively odorless esters frequently 
are added to essential oils to increase the apparent ester content. For- 
tunately, most such esters are high boiling and permit of easy separation. 
The best general method for the detection of such added esters is to separate 
the acids and identify them. Detection of added esters of acetic and formic 

i5 Feigl, "Laboratory Manual of Spot Tests," 193, published by Academic Press Inc., 
New York (1943). 


acid (by isolation and identification of the acids) is not practical since these 
acids usually occur as natural constituents of essential oils. 

Procedure: 196 Saponify 10 cc. of the oil for 2 hr. with 20 cc. 
of 0.5 N alcoholic potassium hydroxide. 197 Add 25 cc. of water 
and evaporate off most of the alcohol. 198 Wash out the un- 
saponified oil by shaking with 3 equal portions of ether. The 
aqueous solution is then made distinctly acid with hydro- 
chloric acid (1:3) and again shaken out with ether. The 
ethereal solution will now contain the relatively insoluble acids, 
such as benzoic, cinnamic, oleic, phthalic, and lauric acid. 
Upon evaporation of the ether these may be recovered. The 
V- aqueous solution will contain the readily water-soluble acids, 
such as citric, oxalic, and tartaric acid. This solution should, 
therefore, be made just alkaline to phenolphthalein and an 
excess of saturated barium chloride solution added. After 
warming for about 10 min., a crystalline precipitate of the in- 
soluble barium salts will be obtained from which the acids can 
be liberated and identified. 

The chemists of Schimmel and Company 199 devised a method for the 
detection of esters of acids which are not readily volatile with steam e.g., 
succinates, citrates, oxalates, and the esters of the higher fatty acids. 

Procedure: Determine the saponification number of the oil 
in the usual manner. Then add a few drops of 0.5 N alcoholic 
sodium hydroxide to the contents of the saponification flask and 
evaporate to dryness on a steam bath. Dissolve the residue in 
5 cc. of water and add 2 cc. of dilute sulfuric acid (1:3). Distill 
off the volatile acids with steam, using the apparatus shown in 
Diagram 4.17. The distillation should be carried out at such 
a rate that a distillate of 250 cc. is collected in the receiver 
at the end of 30 min. ; the volume of the liquid in the saponifica- 
tion flask should be kept at about 10 cc. with the aid of the 
small flame. Collect a further 100 cc. of distillate in a second 
receiver. Add a few drops of a 1% alcoholic phenolphthalein 
solution to each receiver and titrate the free acids with 0.5 N 
potassium hydroxide solution. The first 250 cc. contain most 
of the volatile acids; the next 100 cc. should require only 1 or 2 
drops of the alkali. From the total amount of alkali required 
to neutralize the acids, acid number II is calculated. A large 
difference between the saponification number and acid number 

m p arry> "The Chemistry of Essential Oils," D. Van Nostrand Co., Inc., New York 
(1922), Vol. II, 321. 

197 If the oil has a high ester number, a larger amount of alkali will be required. 

198 Some chemists prefer to evafx>rate to dryness and thei* take up the residue in a 
small amount of water. 

199 Ber. Schimmel & Co., October (1910), 43. 


II indicates the presence of esters of acids only slightly volatile 
with steam. 200 

The presence of the high boiling glyceryl acetates is not revealed by 
either of the procedures described above, since the acid liberated is acetic 
acid, which is volatile with steam, and which occurs naturally in many 
oils (see "Detection pf Ace tins/' p. 338). 

DIAGRAM 4.17. Apparatus for the detection of high boiling esters. 

b. Detection of Phthalates. This method is based upon a preliminary 
saponification of the oil, followed by a separation of phthalic acid as the 
lead salt. The separation is not specific since certain acids other than 
phthalic (e.g., oxalic, citric, and phosphoric) give rise to insoluble lead salts. 
Therefore, it is important to regenerate the acid and determine its melting 

Procedure: 1 Introduce 2 g. of the oil in a 100 cc. saponifica- 
tion flask. Add 25 cc. of an alcoholic sodium hydroxide solu- 
tion prepared by dissolving 1.25 g. of metallic sodium in 100 cc. 
of 95% alcohol. 202 Saponify for 1 hr. Remove and permit the 
flask to cool to room temperature and then immerse it in an ice- 
salt mixture. After standing for 30 min. filter off the precipi- 
tated sodium salts, using a well-cooled Biichner funnel. Wash 

200 This procedure was originally proposed for the examination of bergamot oils; pure 
oils showed a difference between the saponification number and acid number II of not more 
than 7. * 

201 See Naves and Sabetay, "Phthalic Esters," ^Perfumery Essential Oil Record 29 
(1938), 2k 

202 If the oil has a very high ester number, a larger amount of alkali will be required. 


these crystals with ice cold anhydrous alcohol. A precipitate 
at this point may be indicative of any number of organic acids 
(phthalic, salicylic, citric or tartaric). Transfer the salt to a 
250 cc. beaker and dry in an oven at 105 for 2 hr. Cool and 
add 40 to 50 cc. of distilled water and 2 or 3 cc. of glacial acetic 
acid. Heat this solution to the boiling point and add 30 cc. of 
a 10% lead acetate solution. Upon thoroughly cooling in an 
ice bath, the lead salt of phthalic acid will precipitate out al- 
most quantitatively. The lead salts of benzole acid, cinnamic 
acid, and salicylic acid are soluble and remain in the filtrate. 
Separate the lead salt of phthalic acid by filtration. Regen- 
erate the phthalic acid with acid, recrystallize and determine 
the melting point. Phthalic acid melts at about 206 , 203 


Several color reactions have been proposed to distinguish between the 
oil distilled from Mentha piperita L. and the oil from Mentha arvensis L. 
In common with most color reactions, these tests are not always reliable with 
mixtures as complex as essential oils. 

The test described below is the official test of "The United States 
Pharmacopoeia." 204 

Procedure: Mix in a dry test tube 3 drops of oil of pepper- 
mint with 5 cc. of a solution of 1 volume of nitric acid in 300 
volumes of glacial acetic acid, and place the tube in a beaker 
of boiling water. In from 1 to 5 min. the liquid develops a blue 
color which on continued heating deepens and shows a copper 
colored fluorescence and then fades leaving a golden yellow 

The characteristic color changes described in this procedure do not oc- 
cur if an oil distilled from Mentha arvensis L. is examined : the acid solution 
then attains a light yellow color which shows no appreciable change during 
the 5 min. of heating. 

It should be remembered that the color changes described are character- 
istic of the oil from Mentha piperita L. ; mixtures of this oil and Mentha ar- 
vensis L. give the color changes described. Therefore, the test cannot be 
used to detect adulteration with Mentha arvensis L. 

Several other color reactions have been described for these oils in the 


The physical and chemical properties of several common adulterants 
(which have not been thoroughly discussed previously) are briefly noted 
here to aid the essential oil chemist. * 

203 Phthalic anhydride may be formed; the anhydride melts at 131. 

204 Eleventh Revision, 259, 


I. Cedarwood Oil. This is usually found in the last fractions owing to 
the high boiling points of its constituents. 

c?i 6 0.951 to 0.960 

a D -2828' to -3539' 

rc D 20 1.5030 to 1.5059 

Sol. 20 Often insoluble in 10 vol. 90% ale. 

II. Copaiba Oil. This also is found in the last fractions. 

dn 0.901 to 0.905 

D -ll18'to -1422' 

u D 20 1.4972 to 1.4990 

Sol. 20 Insoluble in 10 vol. 90% ale. 

III. Gurjun Balsam Oil. This is a high boiling oil. 

du 0.918 to 0.930 

a D -350' to - 1300' 

n D 20 1.5010 to 1.5050 

Sol. 20 Insoluble in 10 vol. 90% ale. 

The following color reaction for this oil has been recommended: 

To a mixture of 10 cc. of glacial acetic acid and 5 drops of 
concentrated nitric acid, add 5 drops of the oil: gurjun oil gives 
a purple-violet color within 2 min. 

A rather elaborate test has been described by Deussen and Philipp 205 
involving the preparation and isolation of gurjun-ketone semicarbazone 
melting point, 234. 

IV. Fatty Oils. Such oils greatly increase the ester number and evapora- 
tion residue of an oil. They are not volatile with steam, and cannot be dis- 
tilled without decomposition except at exceptionally low pressures. In 
general, they are very insoluble in 90 per cent alcohol and frequently in- 
soluble in 95 per cent alcohol ; castor oil proves an exception, being readily 
soluble in 95 per cent alcohol. The saponified oil frequently shows much 
foaming, owing to the formation of soaps. 


Assurance of the purity of the essential oil is of primary importance in 
an investigation of its chemical constituents. If there is the slightest 
doubt as to whether or not the oil may have been contaminated or adulter- 

206 UeUgs Ann. 369 (1909), 57. 


ated, then such an oil is worthless for the examination, because the results 
obtained after much labor will be open to question. Therefore, it is best 
for the investigator to distill the oil from the botanical, or to supervise the 
distillation in the producing region or factory. Such distillations should be 
carried out on a commercial scale in the manner in which the oil of commerce 
is produced; otherwise, misleading results may be obtained. If this is im- 
possible, the oil should be obtained directly from a prime source of unques- 
tionable repute. 

A representative sample of the oil to be investigated should be analyzed 
carefully. All physical and chemical properties should be determined, 
including specific gravity, optical rotation, refractive index, solubility and 
the percentages of esters, aldehydes, ketones, phenols, acids and alcohols. 
These physicochemical properties should be compared with values given in 
the literature for normal pure oils. Further examination should not be 
attempted if these properties show any suspicious deviation from normal 
values. Such deviation might indicate accidental contamination, adultera- 
tion, or the production of an abnormal oil. 

Although an oil may have been distilled from the proper botanical 
material, nevertheless, it may not represent the normal article of commerce. 
Such factors as the degree of maturity of the botanical frequently exert an 
important influence on the composition of the oil. Consider, for example, 
oil of coriander. If an oil is distilled from the immature and green coriander 
seed it will show a high decyl aldehyde content, sometimes attaining a value 
as high as 70 per cent. As the seed matures, the aldehyde content of the oil 
decreases and the linalool content increases, until finally an oil is obtained 
from mature seed which shows an aldehyde content of about 1 per cent. 
Needless to say, the oil having this low aldehyde content is the oil accepted 
in commerce as normal oil of coriander. 

A further difficulty exists in the proper selection of the botanical. 
Sometimes there are many species within a plant family but only one or 
more yields the desired oil or oils ; the eucalypts are a good example. Oc- 
casionally there are found several varieties of the same species which may 
yield different oils upon distillation. The production of juniper berry oil 
from Juniperus communis L. growing in America gives rise to an oil which 
differs from the normal commercial product formerly obtained from Juni- 
perus communis L. grown in Central Europe. This has been explained by 
the fact that the American oil is distilled from a variety of the true Juniperus 
communis L.; viz., Juniperus communis L. var. depressa Pursh. Physio- 
logical varieties of the same species of certain plants are also known (e.g., 
Eucalyptus dives) . * 

The geographical location of the growing section may exert an effect 
upon the composition and quality of the oil. This probably results from the 


nature of the soil, the altitude at which the plant grows, as well as factors 
such as intensity of sunlight, rainfall and temperature. 

Consideration should be given to the methods of distillation and pro- 
duction of the commercial oil and to the handling of the botanical before 
distillation. Some plants should be distilled as soon as cut, some after sun 
drying for a day, some after thorough drying in the shade, some after drying 
and storage for several years. For details, the reader is referred to the 
section in Chapter III on "Practice of Distillation/' 

All of the above factors should be carefully considered, and as much 
information as possible concerning the botany, geographical source, ma- 
turity, preliminary treatment of the plant material and method of produc- 
tion of the oil should be included in the report on the chemical constituents 
of the oil. 

The amount of oil used for the examination is a limiting factor. The 
availability and the cost of the oil enter in most commercial and academic 
investigations. For oils that are available in relatively unlimited quantity, 
the difficulty of handling large amounts in a research laboratory must be 
considered. Such difficulty may be overcome if the manufacturing plant 
or factory cooperates in the investigation. It then becomes possible to 
fractionate large quantities of the oil, even hundreds of pounds, and to 
investigate the individual fractions or aliquot parts of such fractions. Con- 
stituents occurring in minute amounts have been identified by such a pro- 
cedure. Without benefit of this preliminary fractionation, it is difficult 
to handle much more than 15 liters of an oil in the laboratory. 

For an oil which has not been investigated previously, the first step is 
a general examination, followed by an investigation which endeavors to 
discover as many of the constituents as possible. This usually reveals 
those constituents which occur in substantial amounts. Frequently, indi- 
cations of the occurrence of other constituents are thereby obtained, whose 
presence, however, cannot be established conclusively. A subsequent 
investigation directed solely to the isolation and identification of such indi- 
vidual constituents often will prove successful. 

It is obvious that no comprehensive procedure can be given which will 
prove applicable to all essential oils. The following notes are intended 
merely as an aid to the chemist embarked upon such an investigation. From 
a study of the physicochemical properties of the oil, a general plan for the 
investigation is formulated. 

If the oil shows A large percentage of free acids, phenols or carbonyl com- 
pounds it is usually advisable to remove these components before fractiona- 
tion. Any free acids should always be removed before further treatment of 


small amounts, it may be better to fractionate the oil and then separate 
these components from the enriched fraction or fractions. 

Occasionally solid constituents (such as camphor, menthol, safrole, or 
anethole) may be separated from the whole oil by freezing, followed by 
filtration or centrifuging. Since such separations are never quantitative it 
may be advisable to freeze out these components from the enriched fraction 
rather than from the whole oil. If the solid constituents occur in large 
amounts, one may resort to a preliminary freezing, followed by fractiona- 
tion of the filtrate so obtained. The enriched fractions should then be 
frozen and the material thus further separated added to that obtained from 
the original oil. The difficulty of maintaining sufficiently low temperatures 
during the filtration, especially for large amounts of oil, may make a separa- 
tion from the whole oil impractical. In general, for the isolation and 
purification of the various constituents it is necessary to resort to chemical 
methods in addition to purely physical means. 

After such preliminary treatment as indicated above, the oil or residual 
oil should be fractionated. This will result in a separation of the oil into a 
low boiling terpene fraction, and intermediate fraction, a fraction rich in 
oxygenated constituents, a second intermediate fraction, a fraction contain- 
ing the sesquitcrpene constituents, and a distillation residue. The residue 
usually contains polymerization products and high boiling constituents, such 
as azulenic compounds, and the naturally occurring waxes in the case of 
citrus oils obtained by expression. These waxes show a tendency to "fix" 
part of the volatile components. If present to any appreciable extent these 
waxes should be freed from the more volatile components by steam distilla- 
tion or by the addition of a water-soluble glycol (e.g., diethylene glycol), 
followed by vacuum distillation. 206 The latter procedure will remove most 
of the volatile material from the waxes, leaving a relatively inodorous resi- 
due. The glycol may then be removed from the natural constituents by 
washing out with water or sodium chloride solution. 

Should the original analysis show a high ester content it is usually best 
to fractionate the oil before saponification so that the ester may be obtained 
in a state of relative purity for a determination of physical properties. 
Its components may then be identified after saponification. Since the 
corresponding free alcohol usually is present with the ester, saponification 
of the whole oil (followed by fractionation) may be preferable, especially if 
only small amounts of ester are present. 

The treatment of an oil or fraction with reagents for the purpose of 
separating and purifying various constituents may cause drastic changes 
to occur. This may give rise to new chemical compounds not originally 
present as such in the oil. Intra- and intermolecular rearrangements may 


occur as well as degradations and dehydrations. Such possibilities must be 
considered in the evaluation of the final results of the investigation. 

For the identification of individual constituents which have been 
separated and purified from the oil, two general procedures are employed : 
(1) The determination of physical properties including melting point (or 
congealing point), boiling point, specific gravity, optical rotation, refractive 
index and solubility in alcohol of varying strengths. (2) The preparation 
of suitable derivatives, preferably solid compounds of definite melting point 
capable of purification by recrystallization. In general, the identification 
may be considered established if no depression is observed in the melting 
point when a derivative of the constituent is mixed with the corresponding 
derivative of a sample of known purity and constitution. The reader is 
referred to Volume II on the " Constituents of Essential Oils" for the proper- 
ties of the individual compounds and for data on the melting points of 
certain frequently employed derivatives. In many cases compounds ob- 
tained by oxidation, reduction, and condensations may be used for iden- 

Other methods are often employed in establishing the identity of a 
constituent or derivative : combustion to determine the percentage of carbon 
and hydrogen and to establish the empirical formula; molecular weight 
determinations, especially by cryoscopic methods ; molecular refraction ; ig- 
nition of metallic salts, especially the silver salts of organic acids; determi- 
nations of the percentage of halogen in chlorides and bromides; and other 

Detailed procedures for the separation of chemical groups and for the 
isolation and purification of individual constituents are given in Volume II 
dealing with the "Constituents of Essential Oils." 


The references given in the following pages do not represent a complete 
survey of the literature; they are intended merely as a guide for those in- 
terested in pursuing further the study of analytical procedures applied to 
essential oils and related products. 

Frequently the citation does not refer to the initial article by an author, 
but to a later publication which includes modifications and improvements. 

In this list, there have been included the following : 

1. Established methods which have been superceded by other procedures. 

2. New methods as yet not thoroughly established or investigated. 

3. Important methods which do not have general value for routine 

4. Suggested modifications of well-known methods. 


5. Criticisms of suggested methods. 

6. Evaluations of methods, often with comparative data. 

7. Several reviews, which have added value because of their references 
to the literature. 

The author assumes no responsibility as to the reliability of these methods. 

Sampling and Storage. 

Analysis of oils of sweet orange and lemon. Mechanism and evaluation 
of their deterioration or alteration. Y. R. Naves, Parfums France 10 (1932), 
225. Chem. Abstracts 26 (1932), 5704. 

Analysis of oil of lemon and oil of sweet orange. Measuring the de- 
terioration of the oils by oxidation. Y. R. Naves, Parfums France 12 (1934), 
314. Chem. Abstracts 29 (1935), 2307. 

Standard methods of sampling. W. W. Scott, "Standard Methods of 
Chemical Analysis/' D. Van Nostnmd Co., Inc., (1939), 5th Ed., 1301. 

Carbon}'! and peroxide number in the analysis of ethereal oils. Y. R. 
Naves, Fette u. tieifen 48 (1941), 677. Chem. Zentr. II (1942), 109. Chem. 
Abstracts 37 (1943), 6409. 

Determination of stability of oils and fats. N. D. Sylvester, L. H. 
Lampitt and A. N. Ainsworth, J. Soc. Chem. Ind. 61 (1942), 165. Chem. 
Abstracts 37 (1943), 2599. 

Specific Gravity. 

Change in the specific weight of ethereal oils by heat. K. Irk, Pharm. 
Zentralhalle 55 (1914), 831. Chem. Abstracts 9 (1915), 509. 

Optical Rotation. 

Optical rotation and chemical constitution. Werner Kuhn, Ber. 63B 
(1930), 190. Chem. Abstracts 24 (1930), 1554. 

Effect of solvents on the optical rotation of menthene, bornylene and 
borneol. Irene M. McAlpine, J. Chem. Soc. (1932), 543. Chem. Abstracts 
26 (1932), 2905. 

Molecular dispersion, refractive index, and rotatory power. Value 
in the study and chemical analysis of essential oils. A review. Y. R. Naves, 
Parfums France 10 (1932), 253. Chem. Abstracts 27 (1933), 372. 

Rules of optical rotation arid their application to the investigation of 
constitution and configuration. Karl Freudenberg, Ber. 66B (1933), 177. 
Chem. Abstracts 27 (1933), 2418. 

The simplest principles and laws of optical rotation. Werner Kuhn, 
Ber. 66B (1933), 166. Chem. Abstracts 27 (1933), 2418. 

Measuring rotatory dispersion in the ultraviolet range by photoelectric 
polarimetry. Y. R. Naves, Parfums France 11 (1933), 185. Chem. Ab- 


stracts 28 (1934), 3181. Use of Brulat and Chatelain's photoelectric polarim- 
eter. Y. R. Naves, Chem. Abstracts 26 (1932), 5455, 5847. 

The accurate determination of the rotatory power of essential oils. 
Y. R. Naves and M. G. I., Parfums France 13 (1935), 253. Chem. Abstracts 
30 (1936), 572. 

Identification of essential oils by the effect of solvents on their rotatory 
powers. Y. R. Naves and B. Angla, Compt. rend. 213 (1941), 570. Chem. 
Abstracts 37 (1943), 3877. 

Determination of ethereal oils by changes in optical rotation. Y. R. 
Naves, Fette u. Seifen 49 (1942), 183. Chem. Abstracts 37 (1943), 6405. 

Optical activity of terpenes. Influence of solvent on rotation of bornyl 
and isobornyl methyl ethers. W. Hiickel, H. Kaluba, Liebigs Ann. 550 
(1942), 269. Chem. Abstracts 37 (1943), 3421. 

Refractive Index. 

Change in the refractive index of ethereal oils by heat. K. Irk, Pharm. 
Zentralhalle 55 (1914), 789. Chem. Abstracts 9 (1915), 509. 

Immersion liquids for determining refractivity of solid substances by the 
embedding method. A. Mayrhofer, Mikrochemie 3 (1931), 52. Chem. 
Abstracts 25 (1931), 1417. 

Evaporation Residue. 

Determination of residue on evaporation of essential oils, fitablisse- 
ments Antoine Chiris, Parfums France 10 (1932), 114. Chem. Abstracts 26 
(1932), 4413. 

Flash Point. 

W. W. Scott, "Standard Methods of Chemical Analysis," D. Van Nos- 
trand Co., Inc., New York (1939), Vol. II, 1744, 1752, 1732. 

Determination of Acids. 

Identification of organic acids by partition between ethyl ether and 
water. O. C. Dermer and V. H. Dermer, J. Am. Chem. Soc. 65 (1943), 
1653. Chem. Abstracts 37 (1943), 5697. 

Determination of Esters. 

Procedure for the examination of the ethers (esters) of essential oils. 
B. Angla, Ann. chim. anal. chim. appl 18 (1936), 145. Chem. Abstracts 30 
(1936), 5723. 

Determination of Alcohols. 

Quantitative determination of the active hydrogen in organic compounds. 
T. Zerevitinov, Bw. 41 (1908), 2233. Chem. Abstracts 2 (1908), 2810. 


Quantitative estimation of hydroxy, amino and imino derivatives of 
organic compounds by means of the Grignard reagent, and the nature of 
the changes taking place in solution. H. Hibbert, Proc. Chem. Soc. 28 
(1912), 15. J. Chem. Soc. 101 (1912), 328. Chem. Abstracts 6 (1912), 1744. 

Notes on the acetification (acetylation) of Java citronella oil. T. H. 
Durrans, Perfumery Essential Oil Record 3 (1912), 123. Chem. Abstracts 6 
(1912), 2975. 

New color reaction for alcohols and alcoholic hydroxy groups. L. 
Rosenthaler, Chem. Ztg. 36 (1912), 830. Chem. Abstracts 6 (1912), 3251. 

Use of pyridine as a solvent in the estimation of hydroxyl groups by 
means of alkyl magnesium halides. A. P. Tanberg, /. Am. Chem. Soc. 36 
(1914), 335. Chem. Abstracts 8 (1914), 1277. 

Magnesium organic method for the determination of hydroxyl groups. 
T. Zerevitinov, Ber. 47 (1914), 1659. Chem. Abstracts 8 (1914), 2728. 

Pyridine as solvent in the determination of active hydrogen in organic 
compounds by means of methyl magnesium iodide. T. Zerevitinov, Ber. 
47 (1914), 2417. Chem. Abstracts 9 (1915), 75. 

Formic acid as a reagent in essential oil analysis. W. H. Simmons, 
Analyst 40 (1915), 491. Chem. Abstracts 10 (1916), 664. 

Determination of alcohols by acetylation. Anon., Perfumery Essential 
Oil Record 7 (1916), 374. Chem. Abstracts 11 (1917), 866. 

Determination of alcohols in essential oils. T. T. Cocking, Perfumery 
Essential Oil Record 9 (1918), 37. Chemist Druggist 74 (1913), 87. Chem. 
Abstracts 12 (1918), 1102. 

Determination of volatile alcohols. A. Grim and T. Wirth, Z. deut. 
01- Fettrlnd. 41 (1921), 145. Chem. Abstracts 15 (1921), 1869. 

Pharmacopoeial assay for alcohols in santal oil to include the true acetyl 
value. C. Harrison, J. Assocn. Official Agr. Chem. 4 (1921), 425. Chem. 
Abstracts 15 (1921), 2333. 

Determination of alcohols and phenols in ethereal oils by acetylation with 
pyridine (especially santalol, menthol, eugenol). H. W. van Urk, Pharm. 
Weekblad 58 (1921), 1265. Chem. Abstracts 15 (1921), 3891. 

Determination of alcohols by acetylizing. Hans Wolff, Chem. Umschau 
29 (1922), 2. Chem. Abstracts 16 (1922), 1374. 

Estimation of easily dehydrated alcohols in essential oils. L. Glichitch, 
Compt. rend. 177 (1923), 268. Chem. Abstracts 17 (1923), 3226. Bull soc. 
chim. 33 (1923), 1284. Chem. Abstracts 17 (1923), 3904. 

A color reaction of the alcoholic hydroxyl. Walter Parri, Giorn. farm, 
chim. 73 (1924), 109. Chem. Abstracts 18 (1924), 2667. 

A reagent for multivalent alcohols. The R-acid or /3-naphthol-3,6- 
disulfonic acid. P. Thomas and A. Misca, Bull soc. stiinte Cluj. 2 (1924), 
224. Chem. Abstracts 19 (1925), 3074. 


Determination of alcohols and phenols in ethereal oils by means of mag- 
nesium methyl iodide. T. Zerevitinov, Z. anal. Chem. 68 (1926), 321. 
Chem. Abstracts 21 (1927), 153. 

Notes on the determination of total alcohols in oil of citronella. Justin 
Dupont and Louis Labaune, Chim. ind. 17 (1927), 905. Chem. Abstracts 21 
(1927), 2960. 

Determination of alcohols. A. Verley, Bull. soc. chim. 43 (1928), 469. 
Chem. Abstracts 22 (1928), 3113. 

Determination of phenols and alcohols. A. Verley, Am. Perfumer 24 
(1929), 233. Chem. Abstracts 23 (1929), 4422. 

Detection and identification of primary phenylethyl alcohols in essential 
oils and in mixtures of perfumes. S. Sabetay, Ann. chim. anal. chim. appl. 
11 (1929), 193. Chem. Abstracts 23 (1929), 4770. 

The determination of citronellol and rhodinol in presence of geraniol and 
nerol. L. S. Glichitch and Y. R. Naves, Parfums France 8 (1930), 326. 
Chem. Abstracts 25 (1931), 1033. 

The nitro chromic acid reaction for the detection of primary and second- 
ary alcohols with special reference to saccharides. Wm. R. Fearson and 
David M. Mitchell, Analyst 57 (1932), 372. Chem. Abstracts 26 (1932), 401 1. 

The determination of alcohols in essential oils, fitablissements An- 
toine Chiris, Parfums France 10 (1932), 114. Chem. Abstracts 26 (1932), 

Citronella oil, critical survey on the analytical methods. J. Zimmcr- 
mann, Perfumery Essential Oil Record 23 (1932), 128. Chem. Abstracts 26 
(1932), 5701. 

Determination of alcohols by Zerevitinov's method, fitablissement 
Antoine Chiris, Parfums France 10 (1932), 247. Chem. Abstracts 26 (1932), 

Application of the method of Franchimont to the estimation of the com- 
ponents of essential oils. Marinoa de Mingo, Rev. acad. dene. Madrid 29 
(1932), 150. Chem. Abstracts 27 (1933), 2251. 

Bulgarian otto of rose. E. J. Parry and J. H. Seager, Perfumery Essen- 
tial Oil Record 24 (1933), 149. Chem. Abstracts 27 (1933), 3776. 

Bulgarian otto of roses and its rhodinol content. L. S. Glichitch and 
Y. R. Naves, Parfums France 11 (1933), 154. Chem. Abstracts 27 (1933), 

Estimation of the primary alcohol content of essential oils by phthaliza- 
tion. L. S. Glichitch and Y. R. Naves, Chimie & Industrie, Special No., 
June (1933), 1024. Chem. Abstracts 28 (1934), 575. 

Estimation of primary alcohol content of essential oils L. S. Glichitch 
and Y. R. Naves, Parfums France 1 1 (1933), 235. Chem. Abstracts 28 (1934) , 


Lavender oil from the province of Savona. Andrea Gandini and Teren- 
zio Vignola, Ann. chim. applicata 24 (1934), 431. Chem. Abstracts 29 (1935), 

Rapid determination of primary and secondary alcohols in essential 
oils. S. Sabetay, Compt. rend. 199 (1934), 1419. Chem. Abstracts 29 (1935), 

Analytical results with citronella oils. D. R. Koolhaas, Indische Mer- 
cuur 58 (1935), 429. Chem. Abstracts 29 (1935), 5991. 

The determination of the alcohols in sandalwood oil. R. Delaby and 
Y. Breugnot, Bull. sci. pharmacol. 42 (1935), 385. Chem. Abstracts 29 
(1935), 6699. 

Determination in the presence of tertiary alcohols of the free primary 
and secondary alcohol contents of essential oils by acetylation in pyridine. 
S. Sabetay, Bull soc. chim. [5] 2 (1935), 1716. Chem. Abstracts 30 (1936), 

Determination of tertiary alcohols by cold formylation. S. Sabetay, 
Ann. fals. 39 (1936), 225. Chem. Abstracts 30 (1936), 4787. 

A method for the rapid detection and approximate determination of 
primary alcohols in the presence of secondary and tertiary alcohols by the 
formation of trityl ethers. Se*bastien Sabetay, Compt. rend. 203 (1936), 
1164. Chem. Abstracts 31 (1937), 1728. 

Investigation of monohydric primary, secondary and tertiary alcohols. 
The micro method of determining the rate of esterification. Shunsukc 
Murahashi, Sci. Papers Inst. Phys. Chem. Research (Tokyo) 30 (1936), 272. 
Chem. Abstracts 31 (1937), 3001. 

Simplified procedure for determining primary alcohols by phthalization 
in benzene solution. S6bustien Sabetay and Y. R. Naves, Ann. chim. anal, 
chim. appl 19 (1937), 35. Chem. Abstracts 31 (1937), 2550. 

Simple and rapid procedure for the determination of primary alcohols 
and certain secondary alcohols by hot, pyridinic phthalization and a prac- 
tical technic for identifying esterifiable alcohols in the form of acid phthal- 
atcs. S6bastien Sabetay and Y. R. Naves, Ann. chim. anal. chim. appl. 19 
(1937), 285. Chem. Abstracts 32 (1938), 456. 

Determination of alcohol and phenol functions. Elie Raymond and 
Kmile Bouvetier, Compt. rend. 209 (1939), 439. Chem. Abtsracts 33 (1939), 

Phthalization in hot pyridine. S. Sabetay, Ann. chim. anal. chim. appl. 
2 (1939), 289. Chem. Abstracts 34 (1940), 692. 

Determining alcohols in essential oils. John E. S. Han, Am. Perfumer 
41, No. 2 (1940), 35. Chem. Abstracts 34 (1940), 7066. Am. Perfumer 42, 
No. 6 (1941), 41. Chem. Abstracts 36 (1942), 219. 


lodoform micro test for higher alcohols and ketones. F. Stodola, Ind. 
Eng. Chem., Anal Ed. 15 (1943), 72. Chem. Abstracts 37 (1943), 1673. 

Viscometric method for determining free menthol in peppermint oil. 
L. J. Swift and M. H. Thornton, Ind. Eng. Chem., Anal. Ed. 15 (1943), 422. 
Chem. Abstracts 37 (1943), 5550. 

Periodate reaction applied to cosmetic ingredients. Determination of 
glycerol, ethylene glycol and propylene glycol. Erwin S. Shupe, /. Assocn. 
Official Agr. Chem. 26 (1943), 249. Chem. Abstracts 37 (1943), 5551. 

Volatile plant substances. Application of selective formylation of 
borneol, 3-octanol and benzyl alcohol in the presence of linalool and its 
esters in the analysis of essential oils. Y. R. Naves, Helv. Chim. Acta 27 
(1944), 942. Chem. Abstracts 39 (1945), 1017. 

Estimation of alcohols in essential oils. Y. R. Naves, Perfumery Essen- 
tial Oil Record 36 (1945), 92. Chem. Abstracts 39 (1945), 3119. 

Determination of Aldehydes and Ketones. 

Bisulfite addition compounds. Reinking, Dehnel and Labhardt, Ber. 
38, (1905), 1069. 

The assay of benzaldehyde and oil of bitter almond. F. D. Dodge, 
Orig. Com. 8th Intern. Congr. Appl. Chem. 17, 15. Chem. Abstracts 6 (1912), 

Study of some methods for the determination of aldehydes. B. G. 
Feinberg, Orig. Com. 8th Intern. Congr. Appl. Chem. 1, 187. Chem. Ab- 
stracts 6 (1912), 3251. 

Constitution of the aldehyde and ketone bisulfite compounds. F. 
Raschig, Ber. 59B (1926), 859. Chem. Abstracts 20 (1926), 2816. 

Constitution of aldehyde and ketone bisulfites. F. Raschig and W. 
Prahl, Liebigs Ann. 448 (1926), 265. Chem. Abstracts 20 (1926), 3156. 

The alleged potassium hydroxymethane sulfonate of Max Miiller. F. 
Raschig and W. Prahl, Ber. 59B (1926), 2025. Chem. Abstracts 21 (1927), 223. 

I. Constitution of the aldehyde and ketone bisulfites. G. Schroeter, 
Ber. 59B (1926), 2341. Chem. Abstracts 21 (1927), 386. 

II. Chemical constitution of aldehyde and ketone bisulfites. G. 
Schroeter and M. Sulzbacher, Ber. 61B (1928), 1616. Chem. Abstracts 23 
(1929), 94. 

Microchemical method for determining semicarbazones and its applica- 
tion to the analysis of ketones. Ralph P. Hobson, /. Chem. Soc. (1929), 
1384. Chem. Abstracts 23 (1929), 4648. 

Assay of citronella. F. D. Dodge, Am. Perfumer 24 (1929), 11. Chem. 
Abstracts 23 (1929), 5004. 

A colorimetric method for determination of camphor. Angelo Casti- 
glioni, Ann. chim. applicata 26 (1930), 53. 


Identification of flavoring constituents of commercial flavors. Optical 
properties of the semicarbazones of certain aldehydes and ketones. John 
B. Wilson and George L. Keenan, J. Assocn. Official Agr. Chem. 13 (1930), 
389. Chem. Abstracts 24 (1930), 5431. 

A method for determining aldehydes based on the Cannizzaro and 
Claisen reactions. L. Palfray, S. Sabetay and D. Sontag, Compt. rend. 194 
(1932), 1502. Chem. Abstracts 26 (1932), 4011. 

Determination of aldehydes and ketones in essential oils. H. Schmal- 
fuss, H. Werner and R. Kraul, Z. anal Chem. 87 (1932), 161. Chem. 
Abstracts 26 (1932), 4681. 

Analysis of oils of sweet orange and lemon : I. Observations on the de- 
termination of aldehydes. Y. R. Naves, Parfums France 10 (1932), 198. 
Chem. Abstracts 26 (1932), 5175. 

Hydroxylamine method for determinations of aldehydes and ketones in 
essential oils. R. C. Stillman and R. M. Reed, Perfumery Essential Oil 
Record 23 (1932), 278. Chem. Abstracts 26 (1932), 5702. 

Semimicro method for the determination of cinnamaldehyde in cinnamon 
bark. S. Rivas Goday, Bol. farm, militar 10 (1932), 18. Anales farm, 
bioquim suplemenlo 3, 17. Chem. Abstracts 26 (1932), 5703. 

Determination of compounds containing the carbonyl group by means of 
2,4-dinitrophenylhydrazine. O. Ferniindez and L. Socfas, Rev. acad. dene. 
Madrid 28 (1932), 330. Chem. Abstracts 26 (1932), 4556. 

2,4-Dinitrophenylhydrazine in quantitative determination of carbonyl 
compounds. O. Fernandez, L. Socfas and C. Torres, Anales soc. espafi. fis. 
qutm. 30 (1932), 37. Chem. Abstracts 26 (1932), 2395. 

Description of the Cannizzaro condensation method for determination 
of aldehydes. S. Sabetay, L. Palfray and D. Sontag, Ann. chirn. anal, 
chim. appl. 15 (1933), 251. Chem. Abstracts 27 (1933), 3777. 

New method for determining aldehydes by quantitative Cannizzariza- 
tion. L. Palfray, S. Sabetay and D. Sontag, Chimie & industrie, Special 
No., June (1933), 1037. Chem. Abstracts 28 (1934), 434. 

The determination of aldehydes and ketones with hydroxylamine salt. 
Herrmann Schultes, Angew. Chem. 47 (1934), 258. Chem. Abstracts 28 
(1934), 4336. 

Extension of the Cannizzaro reaction to aliphatic and arylaliphatic 
aldehydes. S6bastien Sabetay and Leon Palfray, Compt. rend. 198 (1934), 
1513. Chem. Abstracts 28 (1934), 4718. 

Detection of aldehydes and ketones in essential oils and drugs. R. 
Fischer and A. Moor, Arch. Pharm. 272 (1934), 691. Chem. Abstracts 28 
(1934), 5597. 

A new number applicable to aldehydes : Cannizzaro number. Applica- 
tion to the assay of bitter almonds. L. Palfray, S. Sabetay and D. Sontag, 


Chimie & Industrie, Special No., April (1934), 863. Chem. Abstracts 28 
(1934), 5927. See also Chem. Abstracts 29 (1935), 2939. 

Application of several methods for the determination of aldehydes in 
essential oils. Maria Anna Schwartz, Ann. chim. applicata 24 (1934), 352. 
Chem. Abstracts 28 (1934), 7419. 

Estimation of aldehydes by the bisulfite method. A. Eric Parkinson 
and E. C. Wagner, Ind. Eng. Chem., Anal Ed. 6 (1934), 433. Chem. 
Abstracts 29 (1935), 427. 

Determination of camphor in galenicals by means of 2,4-dinitrophenyl- 
hydrazine. C. H. Hampshire and G. R. Page, Quart. J. Pharm. PharmacoL 
7 (1934), 558. Chem. Abstracts 29 (1935), 550. 

Influence of free acid on determination of aldehydes and ketones by 
hydroxylamine hydrochloride. L. Palfray and S. Taliard, Compt. rend. 199 
(1934), 296. Chem. Abstracts 29 (1935), 2478. 

Improved hydroxylamine method for the determination of aldehydes 
and ketones. Displacement of oxime equilibria by means of pyridine. 
W. M. D. Bryant and Donald M. Smith, J. Am. Chem. tioc. 57 (1935), 57. 
Chem. Abstracts 29 (1935), 1749. 

The determination of menthone in peppermint essence with hydroxyl- 
amine. G. Parraud, Bull. sci. pharmacol. 42 (1935), 337. Chem. Abstracts 
29 (1935), 5990. 

2,4-Dinitrophenylhydrazine as a quantitative reagent for carbonyl 
compounds. Benzophenone and acetone. G. W. Perkins and Myles W. 
Edwards, Am. J. Pharm. 107 (1935), 208. Chem. Abstracts 29 (1935), 6100. 

A highly sensitive reaction for the characterization and determination of 
citral. J. Bougault and E. Cattelain, J. pharm. chim. 21 (1935), 437. Chem. 
Abstracts 29 (1935), 7578. 

Volumetric determination of camphor by the hydroxylamine method. 
Robert Vandoni and Gerard Desseigne, Bull. soc. chim. [5] 2 (1935), 1685. 
Chem. Abstracts 30 (1936), 56. 

Analysis of essence of cumin. S. Sabetay and L. Palfray, Ann. chim. 
anal chim. appl. 17 (1935), 289. Chem. Abstracts 30 (1936), 240. 

Determination of the carbonyl group in camphor, menthone, pulegone, 
citral and furfural with 2,4-dinitrophenylhydrazine. L. Socias Vifials, Anal, 
acad. Madrid (1935), 1. Analesfarm. bioquim. suppl. 6 (1935), 84. 
Chem. Abstracts 30 (1936), 239. 

Citral and its sulfonates. F. D. Dodge, Am. Perfumer 32, No. 3 (1936), 
67. Chem. Abstracts 30 (1936), 3403. 

Use of 2,4-dinitrophenylhydrazine as a reagent for carbonyl compounds. 
N. R. Campbell, Analyst 61 (1936), 391. Chem. Abstracts 30 (1936), 5534. 

Semicarbazides. w-Tolylsemicarbazide as a reagent for the identifica- 
tion of aldehydes and ketones. Peter P. T. Sah, Si-Min Wang and Chung- 


Hsi Kao, J. Chinese Chem. Soc. 4 (1936), 187. Chem. Abstracts 31 (1937), 

New series of reagents for the carbonyl group, their use for extraction of 
ketonic substances and for microchemical characterization of aldehydes 
and ketones. Andre* Girard and Georges Sandulesco, Helv. Chim. Acta 19 
(1936), 1095. Chem. Abstracts 31 (1937), 1006. 

Determination of camphor in the form of 2,4-dinitrophenylhydrazine in 
concentrated and in weak tinctures of camphor. Maurice-Marie Janot and 
Marcel Mouton, J. pharm. chim. 23 (1936), 547. Chem. Abstracts 31 (1937), 

Use of the reagent of Girard and Sandulesco for the isolation of ketones 
from volatile and animal drugs. G. Sandulesco and S. Sabetay, Riechstoff 
Ind. Kosmetik 12 (1937), 161. Chem. Abstracts 31 (1937), 8822. 

Determination of camphor in alcoholic solutions by the dinitrophenyl- 
hydrazine method. Elmer M. Plein and Charles F. Poe, Ind. Eng. Chem., 
Anal Ed. 10 (1938), 78. Chem. Abstracts 32 (1938), 2686. 

Determination of carbonyl compounds by means of hydroxylamine 
hydrochloride. A. Rcclaire and R. Frank, Perfumery Essential Oil Record 
29 (1938), 212. Chem. Abstracts 32 (1938), 8302. 

Simplified procedure for the analytical oximation of aldehydes and 
ketones. S. Sabetay, Bull. soc. chim. [5] 5 (1938), 1419. Chem. Abstracts 
33 (1939), 1268. 

Notes on analysis of essential oils. Francis D. Dodge, Am. Perfumer 
40, No. 5 (1940), 41. Chem. Abstracts 34 (1940), 4862. 

Benzylideneaminomorpholine compounds (for identification of aromatic 
aldehydes). L. Dugan, Jr., and H. Haendler, J. Am. Chem. Soc. 64 (1942), 
2502. Chem. Abstracts 37 (1943), 130. 

Vanillin determination. D. T. Englis and D. J. Hanahan, Ind. Eng. 
Chem., Anal. Ed. 16 (1944), 505. 

Detection of a-dicarbonyl compounds. C. A. Tarnutzer, L. A. Rittschof 
and C. S. Boruff, hid. Eng. Chem., Anal Ed. 16 (1944), 621. 

A study of the determination of some official aldehydes. M. E. Martin, 
K. Kelly and M. Green, /. Am. Pharm. Assocn. (Sci. Ed.) 35 (1946), 220. 

Determination of Phenols. 

Quantitative determination of carvacrol and thymol in volatile oils. 
Kremers and Schreiner, Pharm. Rev. 14 (1896), 221. 

New bromine method for the determination of aromatic phenols. Its 
special application to thymol. A. Seidell, J. Wash. Acad. Sci. 1, 196. 
Chem. Abstracts 6 (1912), 203. 

Identification of phenols in essential oils. R. M. Reed, Perfumery 
Essential Oil Record 24 (1933), 190. Ctiem. Abstracts 27 (1933), 4346. 


Identification of phenols with 2,4-dinitrochlorobenzene. R. W. Bost 
and Frank Nicholson, J. Am. Chem. Soc. 57 (1935), 2368. Ghent. Abstracts 
30 (1936), 1761. 

Detection and determination of thymol and carvacrol in essential oils. 
Y. Mayor, Parfumerie moderne 31 (1937), 5. Chem. Abstracts 31 (1937), 

Determination of Cineole. 

Determination of cineole in eucalyptus and cajuput oils. C. T. Bennett, 
Chemist Druggist 72 (1908), 55. Chem. Abstracts 2 (1908), 1325. 

The determination of cineole (eucalyptol) in eucalyptus oils. O. Wie- 
gand and M. Lehmann, Chem. Ztg. 32 (1908), 109. Chem. Abstracts 2 
(1908), 1855. 

Estimation of cineole by the resorcinol method. C. T. Bennett, Per- 
fumery Essential Oil Record 3 (1912), 269. Chem. Abstracts 7 (1913), 863. 

Notes on the determination of the cineole content of eucalyptus oils. 
G. A. Harding, Analyst 39 (1914), 475. Chem. Abstracts 9 (1915), 510. 

Estimation of cineole in oil of eucalyptus. J. L. Turner and R. C. 
Holmes, Am. J. Pharm. 87 (1915), 101. Chem. Abstracts 9 (1915), 1093. 

Determination of eucalyptol in eucalyptus oils. C. T. Bennett and 
M. S. Salamon, Perfumery Essential Oil Record 10 (1919), 211. Chem. 
Abstracts 14 (1920), 1001. 

A new method for the estimation of cineole in eucalyptus oil. T. T. 
Cocking, Pharm. J. 105 (1920), 81. Chemist Druggist^93 (1920), 1032. 
Chem. Abstracts 14 (1920), 2967. 

Eucalyptol determination. C. T. Bennett and M. S. Salamon, Per- 
fumery Essential Oil Record 11 (1920), 302. Chem. Abstracts 15 (1921), 146. 

0-Cresol method for eucalyptol determination. C. T. Bennett and M. S. 
Salamon, Perfumery Essential Oil Record 12 (1921), 11. Chem. Abstracts 15 
(1921), 1188. 

Cresineol method for the determination of cineole. T. T. Cocking, 
Perfumery Essential Oil Record 12 (1921), 339. Chem. Abstracts 16 (1922), 

Cresineol method for the determination of cineole. C. E. Sage and 
J. D. Kettle, Perfumery Essential Oil Record 12 (1921), 44. Chem. Ab- 
stracts 15 (1921), 1597. 

Determination of cineole in essential oils. G. Walker, J. Soc. Chem. 
Ind. 42 (1923), 497T. Chem. Abstracts 18 (1924), 566. 

Estimation of cineole in essential oils by the Cocking process. L. S. 
Cash and C. E. Fawsitt, J. Proc. Roy. Soc. N. S. Wales 57 (1923), 157. 
Chem. Abstracts 18 '(1924), 1730. 


Determination of cineole in essential oils. a-Naphthol method. T. T. 
Cocking;, Perfumery Essential Oil Record 15 (1924), 10. Chem. Abstracts 18 
(1924), 1030. 

Phosphoric acid method for cineole in eucalyptus oils. R. E. Shapter, 
Perfumery Essential Oil Record 15 (1924), 423. Chem. Abstracts 19 (1925), 

Color test for cineole. E. J. Schorn, Perfumery Essential Oil Record 16 
(1925), 83. Chem. Abstracts 19 (1925), 17.54. 

Estimation of cineole. Determination of cineole in camphor oils. 
T. T. Cocking, Perfumery Essential Oil Record 18 (1927), 254. Chem. 
Abstracts 21 (1927), 3252. 

Cineole determination. J. Allan, Cliemist Druggist 107 (1927), 615. 
Chem. Abstracts 22 (1928), 2638. 

Occurrence of a number of varieties of Eucalyptus dives as determined by 
chemical analysis of the essential oil. II. With remarks on the o-cresol 
method for estimation of cineole. A. R. Penfold and F. R. Morrison, J. 
Proc. Roy. 8oc. N. 8. Wales 62 (1928), 72. Perfumery Essential Oil Record 
19 (1928), 468. Chem. Abstracts 23 (1929), 475. 

Estimation of cineole in eucalyptus oil. P. A. Berry, Australasian J. 
Pharm. (1929), 203. Chem. Abstracts 23 (1929), 3302. 

The determination of cineole in cajuput oil. A. Reclaire and D. B. 
Spoelstra, Ber. Afdeel. Handelsmuseum Ver. Koloniaal Inst. No. 54 (1930), 8. 
Chem. Abstracts 25 (1931), 2521. 

Determination of cineole in essential oils. Second report. John Allan, 
et al., Analyst 56 (1931), 738. Chem. Abstracts 26 (1932), 255. 

Determination of cineole in eucalyptus oils. A. T. S. Sissons, Soc. 
Chem. Ind. Victoria, Proc. 32 (1932), 681. Chem. Abstracts 27 (1933), 565. 

Determination of cineole in eucalyptus oil. P. A. Berry and T. B. 
Swanson, Australian New Zealand Assocn. Advancement Sci. Sydney Meet- 
ing, August (1932), 15. Chem. Abstracts 27 (1933), 1991. 

New molecular compounds of eucalyptoi. F. D. Dodge, J". Am. Pharm. 
Assocn. 22 (1933), 20. Chem. Abstracts 27 (1933), 2142. 

The determination of the freezing point of a mixture of pure o-cresol 
and pure cineole in molecular proportions. P. A. Berry and T. B. Swanson, 
Australasian J. Pharm. 14, 550. Perfumery Essential Oil Record 24 (1933), 
224. Chem. Abstracts 27 (1933), 4975. 

Macro-, micro-, and histochemical detection of cineole. R. Wasicky and 
E. Gmach, Scientia Pharm. 5 (1934), 113. Chem. Abstracts 29 (1935), 1577. 

Allyl Isothiocyanate. 

Assay of mustard oil and mustard essence. Gadamer, Arch. Pharm. 
237, 110. Chem. Zentr. II (1899), 457. 


Assay of mustard oil and mustard essence. Griitzner, Arch. Pharm. 237, 
110. Chem. Zentr. I (1899), 1227. 

Assay of volatile mustard oil. P. Roeser, J. pharm. chim. [6] 15 (1902), 
361. Chem. Zentr. I (1902), 1254. 

The volumetric assay of allyl mustard oil. M. Kuntze, Arch. Pharm. 
246 (1908), 58. Chem. Abstracts 2 (1908), 1857. 

New process of the determination of allyl mustard oil in powdered black 
mustard. R. Meesemaecker and J. Boivin, J. pharm. chim. [8] 11 (1930) 
478. Chem. Abstracts 25 (1931), 771. 

Estimation of mustard oil in semen sinapis via the D. A. B. 6. Hans 
Kaiser and Otto Leeb, Silddeut. Apoth. Ztg. 73 (1933), 612. Chem. Ab- 
stracts 28 (1934), 256. 

Determination of allyl mustard oil in mustard flour. R. Gros and G. 
Pichon, J. pharm. chim. [8] 19 (1934), 249. Chem. Abstracts 28 (1934), 5179. 

Simple volumetric estimation of mustard oil in spiritus sinapis. H. 
Kaiser and E. Fiirst, Apoth. Ztg. 50 (1935), 1734. Chem. Abstracts 30 
(1936), 1177. 

Determination of Ascaridole. 

Oil of chenopodium and ascaridole. Y. R. Naves, Parfums France 13 
(1935), 4. Chem. Abstracts 29 (1935), 2663. 

Determination of Methyl Anthranilate. 

Rapid identification of methyl anthranilate. S. Sabetay, Ann. fals. 28 
(1935), 478. Chem. Abstracts 30 (1936), 702. 

Determination of Essential Oil Content of Plant Material. 

Apparatus for the determination of volatile oil. J. F. Clevenger, J. Am. 
Pharm. Assocn. 17 (1928), 346. Chem. Abstracts 22 (1928), 2439. 

Rapid determination of ethereal oils in alcoholic solutions. G. Rosen- 
berger, Parfumeur 3 (1929), 78. Chem. Abstracts 23 (1929), 5542. 

Assay of drugs yielding volatile oils. G. R. A. Short, Perfumery Essen- 
tial Oil Record 22 (1931), 208. Chem. Abstracts 25 (1931), 5245. 

The estimation of volatile oil in cloves. L. G. Mitchell and S. Alfend, 
J. Assocn. Official Agr. Chem. 15 (1932), 293. Chem. Abstracts 26 (1932), 

Simplified determination of essential oils in plants. A. S. Ginzberg, 
Khim. Farm. Prom. 8-9 (1932), 326. Chem. Abstracts 27 (1933), 372. 

Estimation of essential oils in drugs and plant material. R. Wasicky, 
G. Rotter and T. Alber, Pharm. Presse, Wi$s.-prakt. Heft (1933), 57. Chem. 
Abstracts 27 (1933), 3557. 

Estimation of essential oils in drugs. Gerhard Schoiz, Apoth. Ztg. 49 
(1934), 1690. Chem. Abstracts 29 (1935), 1577. 


Estimation of essential oil in drugs. Horkheimer, Pharm. Ztg. 80 (1935), 
148. Chem. Abstracts 29 (1935), 2660. 

Determination of the essential oil content and yield of plants and drugs. 
Y. R. Naves and M. G. I., Parfums France 13 (1935), 197. Chem. Abstracts 
29 (1935), 7583. 

Improved method for estimation of essential oil content of drugs. T. 
Tusting Cocking and G. Middleton, Perfumery Essential Oil Record 26 
(1935), 207. Chem. Abstracts 29 (1935), 7014. 

Estimation of essential oils in drugs, and the oil content of peppermint, 
sage, fennel and caraway. L. Kofler and G. V. Herrensschwand, Arch. 
Pharm. 273 (1935), 388. Chem. Abstracts 30 (1936), 568. 

Estimation of essential oils in drugs and plant material. R. Wasicky, 
F. Graf and S. Bayer, Scientia Pliarm. 6 (1935), 101. Chem. Abstracts 30 
(1936), 570. 

Essential oil industry of foreign lands. C. A. Browne, J. Chem. Educa- 
tion 11 (1934), 131. Chem. Abstracts 28 (1934), 2125. 

Improved method for the estimation of essential oil content of drugs. 
T. Tusting Cocking and G. Middleton, Quart J. Pfiarm. Phannacol. 8 (1935), 
435. Chem. Abstracts 30 (1936), 813. 

New method for the determination of essential oils in drugs and fluid 
extracts. Hans Kaiser and Elizabeth Ftirst, Suddeut. Apoth.-Ztg. 76 
(1936), 265. Chem. Abstracts 30 (1936), 4269. 

Evaluation of crude drugs containing ethereal oils. H. Theo Mijnhardt, 
Pharm. Weekblad 73 (1936), 791. Chem. Abstracts 30 (1936), 6131. 

The determination of volatile oils in spices. E. L. Krugers Dagneaux, 
Chem. Weekblad 33 (1936), 544. Chem. Abstracts 30 (1936), 8421. 

Estimation of volatile oil in plant material. W. A. N. Mark well, Per- 
fumery Essential Oil Record 27 (1936), 325. Chem. Abstracts 31 (1937), 504. 

Determination of volatile oil in drugs. H. O. Meek and F. G. Salvin, 
Perfumery Essential Oil Record 28 (1937), 274. Chem. Abstracts 31 (1937), 

Estimation of ethereal oils in spices. P. A. Rowaan and A. J. van 
Duuren, Chem. Weekblad 34 (1937), 534. Chem. Abstracts 32 (1938), 4683. 

Determination of volatile oil in drugs. H. O. Meek and F. G. Salvin, 
Quart. J. Pharm. Pharmacol. 10 (1937), 471. Chem. Abstracts 32 (1938), 

Determination of volatile oils in vegetable drugs. Louis Goldberg, R. K. 
Snyder, E. H. Wirth and E. N. Gathercoal, J. Am. Pharm. Assocn. 27 
(1938), 385. Chem. Abstracts 32 (1938), 7668. 

Estimation of essential oil in drugs. O. Moritz, Arch. Pharm. 276 (1938), 
368. Chem. Abstracts 32 (1938), 8690. 


A simple apparatus for the estimation of the essential oil content of 
vegetable, drugs and spices. Yu Hsieh and Ying Hung, J. Chinese Chem. 
Soc. 8 (1941), 32. Chem. Abstracts 37 (1943), 221. 

Determination of volatile oils in drugs with the aethometer. Zd. 
Zachystal, Chem. Listy 35 (1941), 231. Chem. Abstracts 37 (1943), 3224. 

The elucidation of essential oil compositions. M. M. Rama Rao, Soap, 
Perfumery and Cosmetics 15 (1942), 214. Chem. Abstracts 37 (1943), 500. 

Comparative study of the determination of volatile oils in medicinal 
and spice plants. K. H. Bauer and L. R. Pohloudek, Pharm. Ind. 9 (1942), 
181. Chem. Zentr. II (1942), 1066. Chem. Abstracts 37 (1943), 5194. 

A comparison of the methods for determining the percentages of volatile 
oils in drugs. R. Holdermann and H. Pfiiffle, Deut. Apoth.-Ztg. 57 (1942), 
142. Chem. Zentr. II (1942), 810. Chem. Abstracts 37 (1943), 5555. 

Determination of essential oils in plant material. K. H. Bauer and R. 
Pohloudek, Pharm. Zentralhalle 84 (1943), 223. Chem. Abstracts 39 (1945), 

Determination of Water Content. 

The solubility of water in essential oils. J. C. Umney and S. W. Bunker 
Perfumery Essential Oil Record 3 (1912), 101, 197. Chem. Abstracts 6 
(1912), 2487, 2976. 

The quantitative determination of water in substances by means of 
alkyl magnesium halogen compounds. Th. Zerewitinoff, Z. anaL Chem. 
50, 680. Chem. Abstracts 6 (1912), 203. 

Preliminary notes on the direct determination of moisture. G. L. 
Bidwell and W. F. Sterling, Ind. Eng. Chem. 17 (1925), 147. Chem. Ab- 
stracts 19 (1925), 620. 

The normal moisture content of essential oils. L. S. Glichitch, Parfums 
France 34 (1925), 351. Chem. Abstracts 20 (1926), 798. 

Determination of moisture in essential oils. R. M. Reed, Oil and Soap 
9, No. 3 (1932), 66. Chem. Abstracts 26 (1932), 2555. 

Determination of moisture in aromatic hydrocarbons. Yu. L. Khmel'- 
nitskil, A. I. Doladugin and A. V. Guseva, Zavodskaya Lab. 11 (1945), 534. 
Chem. Abstracts 40 (1946), 2417. 

Test for Heavy Metals. 

Detection and determination of traces of metals in essential oils, con- 
cretes, and enfleurage products. Y. R. Naves, Parfums France 12 (1934), 
89, 116, 139. Chem. Abstracts 28 (1934), 5928. 

The action of essential oils in alcoholic solution on various metals. 
G. A. Rosenberger, Seifensieder-Ztg. 64 (1937), 967. Chem. Abstracts 32 
(1938), 2073, * 


The heavy metals test for volatile oils. Frederick K. Bell and John C. 
Krantz, Jr., ./. Am. Pharm. Assocn. 31 (1942), 533. Chem. Abstracts 37 
(1943), 2136. 

Investigation of the heavy metals test in "The United States Pharma- 
copoeia/' Twelfth Revision. W. W. Edman and C. H. Bundy, Proc. Sci. 
Sect. Toilet Goods Assocn. No. 4 (1945), 28-32, Discussion, 32. CJiem. Ab- 
stracts 40 (1946), 2589. 

Test for Halogens. 

Benzyl alcoholic solutions of potassium hydroxide and their applications. 
Determination of halogens. S6bastien Sabetay and Jean Bigger, Bull. soc. 
chim. 47 (1930), 114. Chem. Abstracts 24 (1930), 2082. 


Determination of safrole in essential oils. Y. Huzita and K. Nakahara, 
J. Chem. Soc. Japan 62 (1941), 5. Chem. Abstracts 37 (1943), 3882. 

Detection of Petroleum. 

The detection of petroleum in ethereal oils. J. Zimmermann, Chem. 
Weekblad 31 (1934), 132. Chem. Abstracts 28 (1934), 2467. 

Methyl and Ethyl Alcohol. 

Determination of ethyl and methyl alcohol in natural essential oils. 
R. Gamier and L. Palfray, Perfumery Essential Oil Record 26 (1935), 259. 
Chem. Abstracts 29 (1935), 6698. 

Presence of methanol and formaldehyde in essential oils and in ethanol 
solutions of essential oils. Y. R. Naves, Parfums France 13 (1935), 60, 91. 
Chem. Abstracts 29 (1935), 5597. 

Detection of High Boiling Esters. 

Detection of diethyl phthalate in spirit. Henry k Szancer, Pharm. 
Zentralhalle 70 (1929), 502. Chem. Abstracts 23 (1929), 5006. 

Analysis of essential oils : determination of ethyl phthalate by K phthal- 
ate method. S. Sabetay, Ann. fals. 28 (1935), 100. Chem. Abstracts 29 
(1935), 3778. 

Phthalic esters detection, identification and determination in essential 
oils, natural perfume substances and synthetic perfumes. Y. R. Naves and 
S. Sabetay, Perfumery Essential Oil Record 29 (1938), 22. Chem. Abstracts 
32 (1938), 2687. 

Determination of ethyl phthalate in presence of essential oils, natural 
perfumes and synthetic perfumes. Y. R. Naves and-S. Sabetay, Bull soc. 
chim. [5] 5, (1938), 102. Chem. Abstracts 32 (1938), 2688. 


Detection of Mentha arvensis Oil. 

Detection of Japanese mint oil in peppermint oils. D. C. Garratt, 
Analyst 60 (1935), 369. Chem. Abstracts 29 (1935), 5596. 

The application of the furfural test for mint oils to other essential oils 
D. C. Garratt, Analyst 60 (1935), 595. Chem. Abstracts 29 (1935), 7580. 


The hydrogen number of some essential oils and essential oil products. 
Oils of sassafras, anise, fennel, clove, and pimenta. A. R. Albright, J. Am. 
Chem. Soc. 36 (1914), 2188. Chem. Abstracts 8 (1914), 3838. 

Catalytic hydrogenation of essential oils. L. Palfray and S. Sabetay, 
15th Congr. chim. ind. [Bruxelles, September (1935)] (1936), 762. Chem. 
Abstracts 30 (1936), 5725. 

High-pressure catalytic hydrogenations. Essential oils and esters. L. 
Palfray and S. Sabetay, Bull soc. chim. [5] 3 (1936), 682. Chem. Ab- 
stracts 30 (1936), 4461. 

Special equipment for catalytic hydrogenation at high pressures. L. 
Palfray, Bull soc. chim. [5] 3 (1936), 508. Chem. Abstracts 30 (1936), 3282. 

Methods of diene syntheses and their interest in the chemistry of per- 
fumes. Y. R. Naves, Parfums France 12 (1934), 255. Chem. Abstracts 29 
(1935), 1581. 

The detection and estimation of a-phellandrene in essential oils. A. J. 
Birch, J. Proc. Roy. Soc. N. S. Wales 71 (1937), 54. Chem. Abstracts 31 
(1937), 8109. 

Determination of coumarin in vanilla extract by a modification of the 
steam distillation method. Ira J. Duncan and R. B. Dustman, Ind. Eng. 
Chem., Anal. ed. 9 (1937), 416. Chem. Abstracts 31 (1937), 8057. 

Precise method for the determination of coumarin, meliolotic acid and 
coumaric acid in plant tissue. Willard L. Roberts and Karl P. Link, /. Biol. 
Chem. 119 (1937), 269. Chem. Abstracts 31 (1937), 6286. 

Determination of coumarin in sweet clover. Comparison of the steam 
distillation and alcohol extraction methods. Ira J. Duncan and R. B. 
Dustman, Ind. Eng. Chem., Anal. Ed. 9, (1937), 471. Chem. Abstracts 31 
(1937), 8826. 

Detection of coumarin in drugs. P. Casparis and E. Manella, Pharm. 
Acta Helv. 19 (1944), 158. Chem. Abstracts 39 (1945), 153. 

The determination of coumarin in plant substances. Milos Cerny, 
Chem. Obzor. 18 (1943), 149. Chem. Abstracts 39 (1945), 3328. Chem. 
Zentr. I (1944), 40. 

Coumarin determination. D. T. Englis and D. J. Hanahan, Ind. Eng. 
Chem., Anal. Ed. 16 (1944), 505. Drug & Cosmetic Ind., October (1944), 


A color reaction for coumarin. R. B. Gelchinskaya, Selektsiya i Se- 
menovodstvo No. 6 (1940), 27. Khim. Referat. Zhur. 4, No. 1 (1941), 89. 
Chem. Abstracts 37 (1943), 1673. 

Oil of birch and methyl salicylate: some new color reactions for the 
differentiation of oil of wintergreen. G. N. Watson and L. E. Sayre, J. Am. 
Pharm. Assocn. 3 (1914), 1658. Chem. Abstracts 9 (1915), 512. 

Color reaction of geranium oil and certain commercial rhodinols. S. 
Sabetay, Riechstoff Ind. 8 (1933), 26. Chem. Abstracts 27 (1933), 2530. 

Blue hydrocarbon occurring in some essential oils. Method of separa- 
tion of "azulenes" with mineral acids. A. E. Sherndal, J. Am. Cliem. Soc. 
37 (1915), 167. Chem. Abstracts 9 (1915), 596. 

A color reaction for azulene sesquiterpenes. S. Sabetay and H. Sabetay, 
Compt. rend. 199 (1934), 313. Chem. Abstracts 28 (1934), 6721. 

Determination of methoxyl and ethoxyl groups. C. L. Palfray, Docu- 
mental sci. 4 (1935), 1. Chem. Abstracts 30 (1936), 5150. Chem. Zentr. I 
(1935), 3821. 

The methyl index of some balsams, rosins and drugs of animal origin. 
M. M. Janot and S. Sabetay, Bull. sci. pharmacol. 42 (1935), 529. Chem. 
Abstracts 30 (1936), 1944. 

The determination of methoxyl-ethoxyl. W. W. Scott, "Standard 
Methods of Chemical Analysis," D. Van Nostrand Co., Inc., New York 
(1939), Vol. II, 2527. 

New method of determining relative surface tension (capillary activity). 
Its application to the measurement of essential oils and related substances. 
Arno Miiller, J. prakt. Chem. 134 (1932), 158. Chem. Abstracts 26 (1932), 

Determination of viscosity. W. W. Scott, "Standard Methods of 
Chemical Analysis," D. Van Nostrand Co., Inc., New York (1939), Vol. II, 
1718, 1719, 1724. 

Antimony trichloride, a new reagent for the double bond. S. Sabetay, 
Compt. rend. 197 (1933), 557. 

Reactions of terpenes with antimony trichloride. Victor E. Levine and 
Eudice Richman, Biochem. J. 27 (1933), 2051. Chem. Abstracts 28 (1934), 

The characterization of double bonds by antimony trichloride. R. 
Delaby, S. Sabetay and M. Janot, Compt. rend. 198 (1934), 276. Chem. 
Abstracts 28 (1934), 2321. 

Ethereal oils containing sulfur and their examination. S. L. Malowan, 
Der Parfinneur 4 (1930), 21. Chem. Abstracts 24 (1930), 1703. 

Estimation of the Tillmans chloramine number in essential oils. P. W. 
Danckwortt and J. Hotzel, Arch. Pharm. 275 (1937), 468. Chem. Abstracts 
31 (1937), 8111. 


Raman effect of the terpenes. Some monocyclic terpenes. G. Dupont, 
P. Daure and J. Levy, Bull. soc. chim. 51 (1932), 921. Chem. Abstracts 27 
(1933), 26. 

Citronellol rhodinol isomerism and Raman spectra. Y. R. Naves, G. 
Brus and J. Allard, Compt. rend. 200 (1935), 1112. Chem. Abstracts 29 
(1935), 3465. 

Light scattering, Raman spectra and allied physical properties of some 
essential and vegetable oils. C. Dakshinamurti, Proc. Indian Acad. Sci. 5A 
(1937), 385. Chem. Abstracts 31 (1937), 6070. 

Examination of essential oils by measurement of absorption in the ultra- 
violet. D. van Os and K. Dykstra. J. Pharm. Chim. 25 (1937), 437, 485. 
Chem. Abstracts 31 (1937), 8118. 

Raman spectra of some terpene aldehydes. R. Manzoni-Ansidei, Alii 
accad. Ital.j Rend, classe sci. fis., mat. nat. [7], 1 (1940), 558. Chem. Ab- 
stracts 37 (1943), 831. 

Determination of absolute oil (irone) in concrete oil of iris. L. S. 
Glichitch and Y. R. Naves, Parfums France 9 (1931), 371. Chem. Abstracts 
26 (1932), 2553. 

General Analysis. 

The oxidation assay of essential oils. F. D. Dodge, Orig. Com. 8th 
Intern. Congr. Appl. Chem. 6, 86. Chem. Abstracts 6 (1912), 2976. 

Notes on the anlysis of some essential oils. F. D. Dodge, J. Am. Pharm. 
Assocn. 3 (1914), 1664. Chem. Abstracts 9 (1915), 512. 

Microchemical characterization of essential oils. L. Rosenthaler, 
Pharm. Acta Helv. 1 (1926), 117. Chem. Abstracts 21 (1927), 1870. 

The analysis of perfume ingredients and essential oils with attention to 
their use in toilet preparations. H. P. Kaufmann, J. Baltos and F. Josephs, 
Fette u. Seifen 44 (1937), 506. Chem. Abstracts 32 (1938), 4724. 

Recent progress in chemical methods applied to the functional analysis 
of essential oils. S. Sabetay and Y. R. Naves, Compt. rend. 17th Congr. 
chim. ind.j Paris, September-October (1937), 777. Chem. Abstracts 32 
(1938), 6805. 

Specification and analytical evaluation of essential oils and natural 
perfumes. Y. R. Naves, A review and general discussion (1) The value 
of analytical characteristics Perfumery Essential Oil Record 31 (1940), 61. 
(2) Analytical interpretation Ibid., 86. 

Constitutents of essential oils and natural perfumes. Notes on the 
investigation of their nature. Y. R. Naves, A review and discussion. Per- 
fumery Essential Oil Record 31 (1940), 161. 


Analytical assay of perfumery raw material. M. M. Rama Rao, /Soap, 
Perfumery and Cosmetics 14 (1941), 757, 760, 770. Chem. Abstracts 37 
(1943), 226; also 37 (1943), 500. 

The analytic assay of perfumery raw materials. Chemical tests. M. 
M. Rama Rao, Soap, Perfumery and Cosmetics 15 (1942), 37, 52, 99, 114. 
Chem. Abstracts 37 (1943), 500. 

The elucidation of essential oil compositions. M. M. Rama Rao, Soap, 
Perfumery and Cosmetics 15 (1942), 214. Chem. Abstracts 37 (1943), 500. 

Structure of certain acyclic isolates. M. F. Carroll. Perfumery 
Essential Oil Record 38, No. 7 (1947), 226. 


Note. All temperatures in this book are given in degrees 
centigrade unless otherwise noted. 


Essential or, as they are also called, volatile or ethereal oils, find an amaz- 
ingly wide and varied application in many industries for the scenting and 
flavoring of all kinds of consumers' finished products, some of them luxuries, 
most of them necessities in our advanced civilization. Many of these 
products contribute directly to our health, happiness and general well being. 
To underestimate their importance is to disregard entirely the physiological 
advantage of continuing to have available these accustomed necessities of 
our daily life. 

Some volatile oils are more or less powerful external or internal antisep- 
tics, others possess an analgesic, haemolytic, or antizymatic action, still 
others act as sedatives, stimulants and stomachics. The anthelmintic 
properties of certain volatile oils, especially wormseed oil, are well known. 
A great deal has been published on this subject, in books and papers on 
pharmacology, pathology and physiology, especially on the antiseptic and 
bactericidal activities of volatile oils, but many of the findings remain con- 
fusing, contradictory and require further elucidation. Much work will still 
have to be done on this fascinating and promising topic which cannot be 
discussed here as it would exceed by far the scope of this treatise. 1 

Spices with their flavor principles, volatile oils, have been used as flavor- 
ing materials since time immemorial. Yet, not always is it sufficiently 
realized that they are actually indispensable to man in order to bring about 
proper digestion of food. The digestive juices containing digestive enzymes 
such as pepsin, trypsin, lipase, amylase, etc., are secreted into the stomach 
and intestines only when stimulated by the smell and taste of pleasantly 
flavored food. The mouth "becomes watery" and so does the stomach. 
As the individual digests more food with a pleasant taste, more digestive 
juices will be secreted, a fact equally true in the reverse. 

The wide use of volatile oils in perfumes, cosmetics and the scenting of 
soaps hardly needs to be mentioned. 

Increasingly, volatile oils and their aromatic isolates serve also for the 
covering of somewhat objectionable odors, as, for instance, in the case of 
artificial leathers. Acceptable and useful articles can now be made from 
raw materials that were formerly discarded or overlooked because of dis- 

1 The reader is referred to the paper "Physiological Aspects of the Essential Oils," by 
G. Malcolm Dyson.Perfumery Essential Oil Record, Special Number, 21 (1930), 287. 



agreeable odors. In most instances the incorporation of aromatics into 
products such as synthetic rubbers and latices has opened new and profitable 
fields for manufacturers. 

Few people realize that in the course of a single day, from morning to 
night, we use or consume a great variety of volatile oils which originate 
from many corners of the world. All of us thereby contribute to the employ- 
ment of innumerable workers and their families, often primitive peoples 
in distant lands. Frequently these small producers depend for their in- 
come upon our continued use of these oils which have thus become really 
"essential" not only to these growers for their livelihood, but also to our 
industries so that they may be able to manufacture their specialties, many 
of them marketed internationally. The essential oils industry, as such, is 
a small one, apt to be overlooked in the economy of a country. Its total 
yearly turnover may be estimated as amounting to only a few scores of 
millions of dollars, but the turnover of the consumers' finished goods, which 
require small additions of essential oils, reaches into many billions per year. 
Countless is the number of people who are involved in the developing, 
manufacturing, controlling, advertising, marketing and selling of these 

The following list will enumerate some of the various industries employ- 
ing volatile oils, aromatic isolates, or combinations. For convenience sake, 
they are listed alphabetically, not according to importance. While in the 
case of the toilet goods industry, it is possible to group the products as 
belonging to this one industry, such a fine distinction cannot always be 
made with other products. Therefore, the terms "manufacturer" and "in- 
dustry" will have to be applied interchangeably as the groupings may re- 
quire. Neither can a clear line be drawn between the products manufac- 
tured by these various industries. 


Glues Porcelain cements 

Paper and industrial tapes Rubber cements 

Pastes Scotch tapes, etc. 


Cat foods Dog foods, etc. 

Cattle feeds 


Automobile finishing supplies Polishes 

Cleaners Soaps, etc. 



Biscuits Mince meat 

Cakes Pies 

Crackers Pretzels 

Doughnuts Puddings 

Fruit cakes Sandwich fillings, etc. 



Fish Sauces 

Meats Soups, etc. 


Chewing gums Coated gums, etc. 


Catsups Pickled fish 

Celery and other salts Relishes 

Chili sauces Salad dressings 

Mayonnaises Table sauces 

Mustards Vinegars, etc. 


Chocolates Jellies 

Fondants Mints 

Gum drops Panned goods 

Hard candies Soft center candies, etc. 


Dentists 7 preparations Tooth pastes 

Mouth washes Tooth powders, etc. 


Bedbug sprays Naphthalene blocks 

Cattle sprays Paradichlorobenzene blocks 

Cockroach powders Plant sprays 

Fly sprays Rat baits 

Japanese beetle attractants Rodent odor eliminators, etc. 

Mosquito repellents 

Commercial extracts Home extracts, etc. 





Cornstarch puddings 
Dehydrated soups, meats and 

Gelatin desserts 
Mince meats 

Pie fillers 

Prepared cake mixes 

Rennet desserts 


Vegetable oils and fats, etc. 


Furniture polishes 
Laundry soaps 

Ice creams 




Room sprays 


Vacuum cleaner pads, etc. 


Prepared ice cream mixes 
Sherbets, etc. 


Sprays, etc. 

Floor polishes 
Floor waxes 


Scrub soaps 

Sink cleaners 

Sweeping compounds, etc. 


Bolognas Prepared meats 

Frankfurters Sausages, etc 


Bituminous paints 

Casein paints 



Paint and varnish removers 

Paint diluents 

Rubber paints 
Synthetic coatings 
Varnishes, etc. 


Carbon papers Paper bags and food wrappers 

Crayons Printing and writing inks 

Drinking cups Printing paper 

Industrial tapes Typewriter ribbons 

Inking pads Writing paper, etc. 



Baby preparations Lipsticks 

Bath preparations Lotions 

Body deodorants Manicure preparations 

Colognes Powders 

Creams Room and theatre sprays 

Depilatories Rouges 

Eye shadows Sachets 

Facial masks Shaving preparations 

Hair preparations Suntan preparations 

Handkerchief extracts Toilet waters, etc. 



Bluing oils Organic solvents 

Fuel oils Petroleum distillates 

Grease deodorants Polishes 

Greases Sulfonated oils 

Lubricating oils Tar products 

Naphtha solvents Waxes, etc 


Antiacid tablets and powders Liniments 

Cough drops Medicinal preparations 

Elixirs Ointments 

Germicides Patent medicines 

Hospital sprays Tonics 

Hospital supplies Vitamin flavor preparations 

Inhalants Wholesale druggists' supplies, etc. 



Dill pickles Sour pickles 

Fancy cut pickles Sweet pickles, etc. 



Fruit butters Jellies 



Bitters Vermouths 

Cordials Whiskies 

Rums Wines, etc. 


Baby pants Synthetic rubber products of all 

Gloves kinds 

Natural and synthetic latices Toys 

Shower curtains Water proofing compounds, etc. 

Surgical supplies 


Cleaning powders Scrub soaps 

Detergents Shampoos 

Household soaps Sweeping compounds 

Laundry soaps Technical soaps 

Liquid hand soaps Toilet soaps, etc. 


Carbonated beverages Root beers 

Cola drinks Soda fountain supplies 

Fountain syrups Soft drink powders 

Ginger ales Sundae toppings, etc. 


Artificial leather and fabric coatings Sisal deodorants 

Dyes ' Textile chemicals 

Hosiery sizing Textile oils 

Linoleum Upholstery materials 

Oil cloths Water proofing materials, etc. 


Chewing tobaccos Smoking tobaccos 

Cigarettes Snuffs 




Cattle sprays Insect powders 

Deodorants Mange medicines and ointments, etc. 

Dog and cat soaps 


Alcohol denaturing compounds Embalming fluid deodorants 

Candles Optical lenses 

Ceramics War gas simulants, etc. 
Cleaners' products 


From the outset it should be stated that little indeed is known about the 
actual processes which cause the spoilage of an essential oil. Usually it is 
attributed to such general reactions as oxidation, resinification, polymeriza- 
tion, hydrolysis of esters, and to interreaction of functional groups. These 
processes seem to be activated by heat, by the presence of air (oxygen), of 
moisture, and catalyzed by exposure to light and in some cases, possibly by 
metals. There is no doubt that oils with a high content of terpenes (all 
citrus oils, pine needle oils, oil of turpentine, juniper berry, etc.) are particu- 
larly prone to spoilage, due probably to oxidation, and especially resinifica- 
cation. Being unsaturated hydrocarbons, the terpenes absorb oxygen from 
the air. Light seems to be of lesser importance as a factor causing deteriora- 
tion, than is moisture. 

Essential oils containing a high percentage of esters (oil of bergamot, 
lavender, etc.) turn acid after improper storage, due to partial hydrolysis 
of esters. The aldehyde content of certain oils (lemongrass, for example) 
gradually diminishes, yet much more slowly than if the isolated aldehyde 
(citral, in this case) were stored as such. Quite probably the essential oil 
contains also some natural antioxidants, yet unknown, which to a certain 
extent protect the aldehyde while it is contained in the oil. Fatty oils, 
with a few exceptions, are very prone to oxidation, but such spoilage can be 
retarded or prevented altogether by the addition of suitable antioxidants, 
such as hydroquinone or its monomethyl ether. Certain types of essential 
oils, especially those containing alcohols (geranium oil, for example), are 
quite stable and stand prolonged storage. Still others, patchouly and 
vetiver, for instance, improve considerably on aging; in fact, they should be 
aged for a few years before being used in perfume compounds. 

As a general rule, any essential oil should first be treated to remove 
metallic impurities, freed from moisture and clarified, and then be stored 
in well-filled, tightly closed containers, at low temperature and protected 


from light. Bottles of hard and dark colored glass are eminently suitable 
for small quantities of oil, but larger quantities will have to be stored in 
metal drums, heavily tin lined, if possible. A layer of carbon dioxide or 
nitrogen gas blown into the container before it is sealed will replace the layer 
of air above the oil and thereby assure added protection against oxidation. 

Previous to storing, as pointed out, the oil should be carefully clarified 
and any moisture removed as the presence of moisture seems to be one of the 
worst factors in the spoilage of an essential oil. The small lots can be de- 
hydrated quite readily by the addition of anhydrous sodium sulfate, by 
thoroughly shaking, standing and filtration. Calcium chloride must never 
be used for dehydration of an essential oil, as this chemical is apt to form 
complex salts with certain alcohols. Larger commercial lots of oil are not 
always easy to clarify. Some oils, such as vetiver, give a great deal of 
trouble. The simplest procedure is to add a sufficient amount of common 
salt to the lot, to stir the mixture for a while, and to let it stand until the